Childhood friends Mohammed Nahin Ahmed and Yusuf Zubair Sarwar, both 22, from the Handsworth area of Birmingham, travelled to the war-torn country last May after contacting Islamic extremists.
They returned in January only after their families put pressure on them to come home.
Officers from West Midlands Police’s counter-terrorism unit were waiting for them at Heathrow Airport, where they were arrested.
A prosecutor revealed the men ordered books from Amazon as part of their preparation to fight in Syria, including Islam For Dummies, The Koran For Dummies and Arabic For Dummies.
A trial due to start yesterday at London’s Woolwich Crown Court was abandoned when they each admitted one count of engaging in conduct in preparation of terrorism acts contrary to Section 5 of the Terrorism Act.
The charges related to activities abroad and not in the UK.
Sarwar’s family reported him missing to police in May last year after they found a handwritten letter from him revealing he had fled to Syria.
The letter, addressed to his mother Majida Sarwar, detailed his intention to “do jihad” by joining a terrorist group called Kataib al-Muhajireen (KaM), later renamed Kateeba al- Kawthar.
The letter also contained money to pay off his debts and instructions to end his mobile phone contract.
In the weeks before leaving the UK, he faked documents to convince his family he was travelling to Turkey as part of a two-week trip organised by Birmingham City University, where he was a part-time computer science student.
Prosecutor Brian Altman told the court: “Without the mother’s actions, the police would not have been in a position to be waiting for the men on their return.”
Ahmed had told his family he was going on holiday with Sarwar.
In fact, the men had carefully planned a one-way trip to the Syrian battleground via Turkey, after researching and discussing jihad, martyrdom and the enemies of Islam, Mr Altman QC told the court.
In one text exchange, Ahmed urged Sarwar not to kill any innocent people or commit suicide, the court heard.
A police search of the men’s homes while the pair were in Syria revealed an online conversation between Ahmed and a Swedish national fighting with the KaM, during which Ahmed said he wanted to join the terrorist group.
Ahmed was told by a Danish Islamist extremist that jihadis could return to their home countries in the EU to carry out tasks.
Ahmed, who was born in Bangladesh, moved to Britain as a child, while Sarwar, who is of Pakistani descent, was born in Britain.
After their arrest, the pair told police that they travelled to Syria for humanitarian reasons.
But officers found “thousands” of warzone-related images of the men with guns on a digital camera carried by the pair into the UK.
Specialists said the images showed they had been in and around Aleppo, the scene of ongoing fighting between Syrian government troops and rebels.
Traces of “military-grade explosives”, including TNT and nitroglycerin were also found on the men’s clothes and trainers.
Judge Topolski QC said he would not pass sentence until a Court of Appeal decision about a similar case had been heard later this summer.
He described the case as a “grave one”. He told the court that together they “carefully planned a journey from the UK to Turkey and on to Syria to join Islamist rebels fighting the regime of Bashar al-Assad”.
Assistant Chief Constable Marcus Beale, senior officer for counter-terrorism in the West Midlands, said: “These young men went to considerable lengths to hide their plans from their families, who have since suffered a great deal of distress.
“It’s not easy to know everything that a family member is doing all of the time, but we encourage parents to hold a healthy interest and curiosity into who their children mix with and who seems to hold a strong influence over them.”