A passport and a visa are required. Visas must be obtained prior to arrival in Syria from a Syrian diplomatic mission located in the traveler’s country of residence. The Embassy of the Syrian Arab Republic in Washington, DC, however, suspended all operations, including consular services on March 18, 2014 and has not appointed a protecting power.
Foreigners who wish to stay 15 days or more in Syria must register with Syrian immigration authorities by the 15th day of their stay.
Syria charges a departure tax at its land and sea borders for all visitors except those on diplomatic passports and children under the age of 11.
Israel Travel: The Syrian government rigidly enforces restrictions on prior travel to Israel, and does not allow persons with passports bearing Israeli visas or entry/exit stamps to enter the country. Likewise, the absence of entry stamps from a country adjacent to Israel, which the traveler has just visited, will cause Syrian immigration officials to refuse admittance. Overland entry into Syria directly from Israel is not possible. U.S. citizen travelers suspected of having traveled to Israel have been detained for questioning.
Dual Nationality: U.S. males holding dual Syrian citizenship or non-dual U.S. citizen men of Syrian origin, even those born in the United States, may be subject to compulsory military service unless they receive a temporary or permanent exemption from a Syrian diplomatic mission abroad prior to their entry into Syria. Syria usually will not issue visas or residency permits to students wishing to study religion or Arabic in private religious institutions.
A child under the age of eighteen whose father is Syrian or of Syrian descent must have his/her father’s permission to leave Syria, even if the parents are separated or divorced and the mother has been granted full custody by a Syrian court. On occasion, the families of U.S.-Syrian women visiting Syria have attempted to prevent them from leaving the country, generally in order to compel the woman to marry. Although under Syrian law a woman does not need her husband's explicit consent every time she wishes to leave Syria, a Syrian husband may take legal action to prevent his wife from leaving the country, regardless of her nationality. Once such legal orders are in place, the U.S. government cannot help U.S. citizens to leave Syria.
Some HIV/AIDS entry restrictions exist for visitors or foreign residents of Syria. AIDS tests are mandatory for foreigners from ages 15 to 60 who wish to reside in Syria. The AIDS test must be conducted in Syria at a facility approved by the Syrian Ministry of Health. A residence permit will not be issued until the applicant is determined HIV negative. Foreigners wishing to marry Syrian nationals in Syria must also be tested for HIV. Please verify this information with the Syrian government before you travel.
Information from travel.state.gov on Jan 22, 2018