Abstract: The influence of the age and amount of the inoculum on invertase synthesis by Saccharomyces cerevisiae KR18 was studied during submerged cultivation. Fermentation was carried out at 30oC in fermentation medium containing sucrose, yeast extract and peptone at initial pH 6.0 at 200 rpm. The maximum production of invertase (6.9 U ml-1) was obtained when 1.0 ml vegetative inoculum (4 %), developed for 12 h, was used per 25 ml of fermentation medium. The dry cell mass and sugar consumption were 3.0 and 16.18 mg ml-1, respectively. The specific growth and product rates (h-1) are more encouraging to use 4 % vegetative inoculum under optimized conditions.