Background: Syria has experienced war since 2011, leaving over 80% under the poverty line and millions being displaced. War and its retaliations have significantly impacted the mental health of Syrians. This study evaluates the post-traumatic stress disorder (PTSD), and the severity of the mental distress caused by war and other factors such as low social support. This study also evaluates other variables and compare the findings with multiple studies of Syria and refugees. Methods: This is a cross-sectional study that included people who lived in Syria from different provinces. Online surveys on multiple online groups included Kessler 10 (K10) questionnaire, the Screen for Posttraumatic Stress Symptoms (SPTSS) tool, the Multidimensional Scale of Perceived Social Support, and demographic and war-related questionnaires. Results: Our study included 1951 participants, of which, 527 (27.0%) were males and 1538 (78.8%) aged (19-25) years. Among participants, 44% had severe mental disorder, 27% had both severe mental disorder and full PTSD symptoms, 36.9% had full PTSD symptoms, and only 10.8% had neither positive PTSD symptoms nor mental disorder on the K10 scale. Around 23% had low overall support. Half of the responders were internally displaced, and 27.6% were forced to change place of living three times or more due to war. Around 86.6% of the responders believed that the crisis was the main reason for their mental distress. Those with high SPTSS and K10 scores were found to take more days off from work or school due to negative feelings and having somatic symptoms. Moreover, the number of times changing places of living due to war, educational level, and being distressed by war noise were the most important factors for more sever PTSD and mental distress. No differences in PTSD and mental disorder prevalence was noted between provinces or type of job. A strong correlation (r=0.623) was found between SPTSS and K10 scores. Conclusion: The conflict in Syria has left the population at a great risk for mental distress which was more severe compared to Syrian refugees elsewhere. Many measures with an emphasis on mental health are needed to aid the people against a long-term avoidable suffering.