The main purpose of this study is to evaluate which more hygienic denture base for complete denture wearers; (Poly methyl methacrylate or thermoplastic flexible denture base). MATERIAL AND METHODS: Twenty complete dentures were constructed for ten patients, ten manufactured from Poly methyl methacrylate and other ten were constructed from flexible thermoplastic resin material. Three swabs were taken of two dentures for each patient, first swab at zero time, second swab after one weak and the third swab after one month. The swabs were obtained from the palate of the patient and from the fitting surface of upper denture, to find out which type of denture bases were showing more Candida adhesion and bacterial accumulation especially streptococci and staphylococci. RESULTS: In conventional denture the highest mean value was found in (At zero time) followed by (After 4 weeks), while the lowest mean value was found in (At
 1 week).In flexible denture the highest mean value was found in (After 1 week) followed by (After 4 weeks), while the lowest mean value was found in (At zero time). CONCLUSION: Both conventional and flexible dentures induced changes in palatal micro flora and formation of dental plaque but flexible dentures are more because of porosity which act like niches in which microorganism protected even from sheer forces and oral hygiene measures.