Two sets of organotin compounds, that is, one having dibutyl and the other dioctyl groups each with a varying length of a carboxyl group attached to a tin atom, were studied as catalysts for the polycondensation of room temperature vulcanization of hydroxyfunctional polydimethylsiloxane (HOPDMS). The experiments were carried out with the help of a simple and inexpensive piece of equipment called the vibrating needle curemeter (VNC). It has been found that an increase in the length of the carboxyl, as well as the alkyl group bonded to the tin atom, decreases the activity of organotin compounds as catalysts for the polycondensation of HOPDMS. A threshold limit for the difference in catalytic activity of organotin compounds for curing HOPDMS has, for the first time, been established. It has been worked out that when the total number of carbon atoms in the ester and alkyl groups in organotin compounds exceeds 30, then the difference in their catalytic activity reaches a nonmeasurable level by VNC.