He is attending a gathering of the Friends of Syria group of nations that support the Syrian opposition.
Mr Kerry is expected to announce increased "non-lethal" aid for the rebels but not weapons.
The UN estimates 70,000 people have died in the Syrian conflict since 2011.
Mr Kerry says US wants to "accelerate the political transition" in Syria.Specific promises
The main opposition Syrian National Coalition (SNC) had threatened to boycott the meeting in Rome in frustration at the "the world's silence" at the violence.
But it agreed to attend after the US and UK indicated there would be specific promises of aid.
The increased support is expected to involve food and medical supplies for rebel-controlled areas.
It could also include training, armoured vehicles and night-vision equipment, the New York Times reported, citing senior US officials.
Mr Kerry has said he wants to "change the calculation" of President AssadThe Obama administration has so far made it clear that it will not supply weapons to the Syrian rebels.
But arms are clearly what the Syrian opposition want and they are becoming ever more frustrated at the level of help they are getting, BBC diplomatic correspondent Jonathan Marcus says.
According to UN estimates, more that 70,000 people have been killed in Syria since the revolt against President Assad began nearly two years ago.
Opposition fighters have been constantly outgunned as President Assad's forces deploy tanks, aircraft and missiles against them.
The US Secretary of State, who succeeded Hillary Clinton, is on an 11-day tour of Europe and the Middle East.
Speaking in Paris on Wednesday, he said he wanted to hear from the Syrian opposition how best to end the bloodshed.
``We want their advice on how we can accelerate the prospects of a political solution because that is what we believe is the best path to peace, the best way to protect the interests of the Syrian people, the best way to end the killing,'' he said.
The Syrian rebels say weapons are what they need mostBritish Foreign Secretary William Hague has also said the UK is preparing to "significantly increase" its support for Syria's opposition.Russia 'crucial'
Meanwhile, French President Francois Hollande is in Moscow to discuss Syria with Russian President Vladimir Putin.
Russia is a key ally of President Assad, supplying him with weapons and blocking resolutions against him at the UN.
But it also been encouraging the Syrian government to hold direct talks with the opposition and has offered to host negotiations in Moscow.
Speaking before the meeting, President Hollande said Mr Putin had a crucial role to play in efforts to find a political solution to the conflict.
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Most of [the refugees] have lost everything”Antonio GuterresUN High Commissioner for Refugees
"We must finally start the process political dialogue that has not yet begun in Syria," Mr Hollande told Ekho Moskvy radio.
"A lot will depend on President Putin's stance."
Western powers say President Assad must step down as part of any political solution, as do the opposition, but Russia does not agree.
In contrast to the slow pace of diplomatic efforts to end the conflict, the fighting on the ground has continued to escalate, with grave humanitarian consequences.'Tragedy'
On Wednesday UN High Commissioner for Refugees Antonio Guterres said more than 40,000 Syrians were fleeing the country each week, and the total number of registered refugees was approaching one million.
"The refugee numbers are staggering, but they cannot convey the full extent of the tragedy.
"Three-quarters of the refugees are women and children; many of them have lost family members; most of them have lost everything," he told the Security Council.
In some of the latest fighting, activists say government jets bombed rebels who were attacking a police academy outside Aleppo, Syria's second city.
"The rebels are still trying to storm the school, but they can't because the regime is carrying out airstrikes and bombarding rebel forces," said the UK-based Syrian Observatory for Human Rights, a UK-based activist group.
Along with the capital Damascus, Aleppo is a key battleground in the conflict and has seen some of the most intense fighting.
Opposition groups are particularly enraged by what they say is the government's use of Scud missiles to bombard rebel-held areas of the city, causing mass civilian casualties.
