Three trials were conducted using completely randomized designs to evaluate the influence of concentration of thiamine supplementation on honey bee colony growth (brood and adult population) in different seasons. Twenty Iranian honey bee colonies (Apis mellifera meda), divided into 5 experimental groups, were used in the study. Control groups were fed sugar syrup. The experimental colonies were fed in the same manner but with syrup supplemented with different levels of thiamine (100, 200, 300 and 400 ppm). Each diet was tested on a set of four colonies selected for each treatment. Changes in brood areas had significantly difference between colonies fed thiamine (200 ppm) and sugar syrup (control) in summer season (P<0.05). In summer season the lowest brood production occurred in colonies fed sugar syrup. In winter season, adult population sizes and brood areas in colonies fed syrup supplemented with thiamine (200 ppm) were significantly larger than colonies fed sugar syrup (P<0.05). No significant differences were found between treatments on brood area and adult population size in spring season when some pollen was being collected by colonies

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