Background: Photodynamic disinfection is a new efficient specific method of disinfection of the denture surface which should be highly polished with high mechanical properties to prevent further colonization of bacteria that may cause starting from oral stomatitis up to pneumonia. The aim of this study is to investigate the effect of Photodynamic disinfection on milled acrylic flexural strength after 3 years of usage. Material& method: Preparing of 2mm × 2mm × 25mm 50 samples of milled acrylic , applying of a continuous 3 days,19 hours and 15 minute of disinfection = 12 month of use (15 minutes a day) ,7 days, 14 hours and 30 minute = 24 months and finally at the end of the 11 days, 9 hours and 45 minutes day of disinfection which simulate 3 years of disinfection with photodynamic method and compare it with +ve control (1%NaCl disinfection ) and -ve control (distilled water) groups and preparing 50 sample of heat cured acrylic with the same parameters and propose them to the same conditions and comparing them to milled samples then flexural strength is tested after each interval and compared to base line specimens with no disinfection at all . Results: The mean value of each disinfectant group flexural strength show insignificant effect in flexural strength compared to other control groups. Conclusion: From the results of the current study, we found that Photodynamic disinfection can be used safely to disinfect complete dentures but further studies are required due to lack of literature about this field.