1. It was found that fructose 1, 6-diphosphate and fructose 6-monophosphate were accumulated by borate in anaerobic glycolysis system of liver homogenates of guinea pigs. 2. Glyceraldehydephosphate dehydrogenase^*2 (GAP dehydrogenase) from yeast and in liver homogenates of guinea pigs and rats were found to be inhibited by borate. The inhibition was observed in both cases in which free D-glyceraldehyde or D-glyceraldehyde 3-phosphate was used as substrate. 3.GAP dehydrogenase was inhibited competitively by borate, and the inhibition was reversed by dialysis, but not reversed by excess sugars or polyhydroxy compounds in the experimental condition. 4. Borate has no effect on lactate dehydrogenase^*6 from rabbit muscle and also in liver homogenates of guinea pigs. 5. Toxicity of borate was discussed from biochemical point of view.