Effect of nonionic surface active agents on the olive-oil decomposition with pancreatic lipase was examined. Of the agents used, both Brij 35 and Tween 80 activated the olive-oil decomposition in low concentrations but obstructed the decomposition in higher concentrations. Span 80 and 85 showed reverse phenomena, obstructing the decomposition in lower concentrations and activating in higher concentrations. This is chiefly due to the hydrophile-lipophile balance and this was evident from the results obtained by mixing Tween 80 and Span 85 to prepare mixtures of various hydrophile-lipophile balance. Activation agents with large balance activates the enzyme in lower concentrations and inhibits in higher concentrations, while the reverse is true of those with small balance.The same examination was made with anionic surface active agents, sodium dodecylsulfate, and carbowax, but all effected obstruction of decomposition and none showed any activation. The presence of calcium ion was found to make Brij 35 and Tween 80 inhibit enzymatic action even in lower concentrations, while the presence of dextrin and glucose had no effect on Brij 35 and. Tween 80 in an amount five times that of the enzyme. The concentration of Tween 80 in activating pancreatic lipase was found to be affected by the amount of the enzyme rather than that of olive oil.