Objective: The aim of this study is to evaluate the effect of using heat cured thermoelastic acrylic resin as a modification of a posterior palatal seal on the retention of upper complete denture for diabetic patient. Materials and method: 14 controlled diabetic completely edentulous patients were selected from the National Institute of Diabetes (NIDE) to participate in this study. They were divided into two equal groups: Group A: seven patients received conventional heat cured acrylic resin. Group B: seven patients received conventional heat cured acrylic resin with heat cured thermo elastic acrylic resin at post dam area. Result: There was a statistically significant difference between means retention of the two groups (P-value < 0.001). Versacryl showed statistically significantly higher mean retention value than Conventional A.R throughout six months that retention measured at insertion, 3 months &6 months. Conclusion: Both groups A&B (acrylic & versacryl) have shown increased retention qualities over a period at 6 months. The denture with versacryl at post dam more retentive over period of study rather than acrylic denture