Officers said they had arrested a 33-year-old man at London's Gatwick Airport on Wednesday afternoon as he tried to board a plane leaving Britain, while three others, aged 18, 22, and 31 were held at addresses in east London during early morning raids on Thursday.
The men were all detained on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act.
The arrests were linked to an investigation which has already led to two men being charged with terrorism offences over the kidnapping of two photographers in Syria.
Dutch photographer Jeroen Oerlemans and British colleague John Cantlie were taken hostage on July 17 while working near the Syrian border with Turkey. They were released on July 26.
Last year British Foreign Secretary William Hague warned there was evidence that some people in Britain wanted to join the fighting in Syria.