We studied three kinds of ladderlike polyepoxysiloxanes, which have different side groups grafted on the ladderlike backbones. 1,5-Bis(aminopropyl)tetramethyl disiloxane (diamine) was used as the curing agent. The reaction between ladderlike polyepoxysiloxanes and diamine was investigated by contact angle measurements and surface free energy study. Several factors such as diamine amount, reaction time, and temperature can affect the systems' surface tension (or surface free energy), which were determined by two-liquid geometric and three-liquid acid-base methods. The experimental results showed that an increase in the diamine amount in the reaction systems results in an increase in the polar part of surface free energy because of electron donate characteristics of the diamine. However, because epoxy (electron acceptor) and diamine (electron donor) react fast at elevated temperatures, increasing reaction temperature decreases the polar part of the surface free energy, while increases the nonpolar part of the surface free energy. The evolution of surface free energy with time for various epoxy-diamine reaction systems at various temperatures has also been studied. It was found that it took a relatively long time (50-60 h) to reach the equilibrium state. The experimental results can be well interpreted by the epoxydiamine reaction mechanism and van Oss-Good's Lewis acid-base theory.