The effect of sodium phytate on citric acid production was studied. The results showed that sodium phytate had a stimulating role in citric acid accumulation, with a concentration of 1.0% being the best for maximum citric acid production. The addition of sodium phytate to the fermentation medium increased citric acid production and substrate utilization, and inhibited growth. In order to elucidate the stimulating role of sodium phytate on citric acid production, the effect of sodium phytate on the activities of several key enzymes involved in the tricarboxylic acid cycle was studied. Sodium phytate depressed the activity of NADP-isocitrate dehydrogenase and increased pyruvate carboxylase activity, hence favouring accumulation of citric acid. However, in the case of citrate synthase, no significant difference was observed.