Aim of the study: This study was carried out to evaluate the effect of using ultra suction system on mandibular complete denture retention and on the rate of growth of candida albicans. Material and methods: Ten completely edentulous patients participated in this study. Each patient recived two dentures a conventional mandibular denture
(D1 denture) constructed using heat cured acrylic resin and an ultra suction retained denture (D2 denture) which was constructed using heat cured acrylic resin with ultra suction system added to it. Patients were left to function with each denture set for a period one week, one month, three months respectivly during which they were recalled
to test denture retention and to make microbilogical examination. Retention test was conducted using universal testing machine after pulling the denture from it's geographic  centre. The collected records were recorded, tabulated and statistically analyzed for each denture using the paired t test. Results: The mean retention value for (D1 denture)
were 3.66 ±1.07, 3.02±0.82, 4.07± 0.84 , 3.97 ± 0.99 at the baseline and after one week .one month ,three months respectively while for (D2 denture)values were 8.01±2.80 , 8.35± 2.53, 8.72±2.19, 7.11±1.70 at the baseline and after one week .one month ,three months respectively. Statistical analysis of these data revealed a significance increase in
the retention after application of ultra suction system. The mean values for microbilogy test were calculated using Chi square test at the base line and after three months of wearing dentures and after statically analyzing the results, it showed that statistically non-significant difference between conventional (D1) and ultra-suction (D2) denture
(P=0.1286>0.05).