Genetic factors are important in the development of post-traumatic stress disorder (PTSD) following exposure to traumatic events. However, the molecular genetic underpinnings of this disorder have not been definitive. This study examined the association between tryptophan hydroxylase 2 (TPH2) rs11178997 genotype, a single-nucleotide polymorphism (SNP) located in the transcriptional control region, and PTSD symptoms. A total of 326 Chinese adults who suffered from the deadly 2008 Wenchuan earthquake and lost their children during the disaster participated in this study. PTSD symptoms were measured with PTSD checklist, and the SNP was successfully genotyped by the MassARRAY system. The results indicated that, although the rs11178997 genotype was not associated with total PTSD symptoms, it could significantly predict severity of PTSD's avoidance symptoms in women. These findings support that TPH2 may play an important functional role in the development of PTSD and contribute to the limited literature regarding the genetic basis and the sex-specific expression of PTSD's symptoms.