To validate a Postpartum Depression Screening Scale (PDSS) for screening postpartum depressive disorder in Songkhla Thai population, a screening test was conducted. A Thai version of the PDSS was developed using back translation and pre-tested on a prospective cohort of 400 postpartum women at 6-8 weeks from November 2003 to September 2004 in a university hospital, Southern Thailand. The diagnosis of postpartum depression was determined using DSM-IV diagnostic criteria for minor and major depressive disorders. The alpha reliability for the total PDSS was 0.9. The recommended cut-off scores of 51for screening major or minor depressive disorders and of 90 for screening major depressive disorder Area under the receiver operating characteristics (ROC) curve was 0.8 for major and minor depressive disorders and 0.9 for major depressive disorder In conclusion, this is a useful and beneficial instrument as there is no other Thai version validated instrument for postpartum depression.