In this study, we aimed to investigate the effects of boron on in vivo oral yeast colonization in study groups which are exposed to boron dust in different sections of the boron mine. The study was carried out in the boron mining areas of two districts (Eskisehir and Balikesir) of Turkey. We included 184 people working in open quarry and stone milling unit, 144 people working in the factory and 150 people as control group. Specimens were taken from four oral mucosal regions and cultured onto Sabouraud dextrose agar. After incubation for 3-7 days at 30 degrees C, the total number of yeast colonies on the plates was considered the relative intensity of carriage, and the total number of yeast colonies on the plates was considered the relative intensity of oral carriage. The susceptibility of Candida spp. to boric acid was investigated. The frequency of Candida colonization in boron intensive area workers was found significantly higher than automatic factory workers and control groups (p = 0.012), there were no difference between automatic factory workers and control groups in point of Candida colonization (p = 0.749). We observed that oral yeast colonization had increased directly proportional with boron powder exposure in boron mine (p = 0.005). Mean minimum inhibitory concentrations (MICs) of boric acid for Boron intensive area, 0.87-2.0% for automatic factory and 0.83-2.0% for control subjects. We observed that intensive exposure to boron mineral powders was strictly related to oral yeast colonization. Exposure to industrial boron mineral powder may cause important health problems by increasing Candida colonization in oral cavity. It may be useful to do periodical health control in boron mineral workers and population under risk.