The deactivation of a macroporous sulfonic resin in a condensation process with production of water is due to three simultaneous causes : inhibition by water, fouling/poisoning, and hydrolysis of sulfonic groups. The reaction was performed in a batch reactor. The diffusional resistances were negligible for stirrer speed > 100 rpm, and particle size < 0.09 mm. The inhibition by water was minimum with water concentration, C(w), in the range of 0.1-0.2 mol/L. For a greater C(w), the inhibition is expressed by the pseudoactivity a(w) = K1/k(1+k2C(w)2). The deactivation by fouling/poisoning follows third-order kinetics with respect to both the activity, a, and the concentration of byproducts, C(P), -da/dt = k(d)C(P)3a3. The hydrolysis of sulfonic groups, measured by the loss of fractional acid capacity, y(n), follows second-order kinetics, -dy(n)/dt = k(H)y(n)2.