Purpose: to study the effect of using thermo-elastic acrylic resin borders and post-dam on retention of conventional heat cured acrylic resin. Material and Methods: Fifteen completely edentulous patients were selected from the out-patient Clinic of the Removable Prosthodontics Department; Faculty of Oral and Dental Medicine for Girls, Al- Azhar University. On the day of the delivery each patient received maxillary and mandibular complete dentures made of conventional heat cured acrylic resin (Heat cured acrylic resin, Vertex-B. V, Netherlands). A duplicate cast was made for the maxillary complete denture. 15 patients were divided into 3 groups, 5 patients each. The first group wore the conventional heat cured acrylic complete dentures unchanged all the time, for the second group 2-3mm of the entire maxillary denture borders were removed and replaced with the flexible denture base material (Versacryl), without replacing the post dam area, while for the third group only the post dam area was replaced by the flexible denture base material (Versacryl). Results: Pair-wise comparisons between the groups revealed that borders group showed the statistically significant highest mean retention value. Conclusion: Thermo-elastic heat cured acrylic resin (Versacryl) modified dentures exhibit more retention than that of the conventional heat cured acrylic denture.