Altliough esterification reaci,ion hetweeu monobasic acids and monohydric alcculs is a well-known chemical reaction, on which various au bhors, such as Golclschmidt, Hinslielwood, Flory and others, have done much work, but the mechanism of estexification and the or Mcr of the reaction in the absence or presenace of a foreign acid remain unclarified. For this purpose we have studied the kinetics of esterification reactions laetween lauric acid and normal octyl alcohol with eqni- or non-equimolar quantity ratios in the abseence or presence of a foreign acid at different temperatures.