The influence of the thermodynamic activity of water (a(w)) on the synthesis of triolein catalyzed by Mucor miehei lipase was investigated. Its effect on the equilibrium and on the rates of the different reactions present, esterification and mono- and diglyceride isomerization, was evaluated through measurements made in controlled water activity atmosphere. The apparent equilibrium constants were measured from the concentration of the different species as a function of the initial glycerol-to-oleic-acid ratio using all the values at once with a multiresponse nonlinear regression technique. Rate constants were determined from kinetic measurements and nonlinear regression using the variation of the concentration of all significant species in the system. Except for the synthesis of diolein from monoolein, which shows a maximum for a(w) approximate to 0.5, the apparent rate constants of the various reactions are not significantly affected by the value of the water activity. The equilibrium is shifted toward the synthesis of triolein for low values of a(w), indicating that in the design of a process for triglyceride synthesis, using M. miehei lipase as a catalyst, the water activity can be lowered to extreme values to favor the synthesis, without any sacrifice on the productivity of the process.