Aminopropyl-terminated poly(dimethylsiloxane) (ATPS) with different molecular weights was prepared by base-catalyzed equilibration of octamethylcyclotetrasiloxane and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane with different ratios. Their number-average molecular weights (M-n) were determined by end-group analysis, and intrinsic viscosity([eta]) in toluene was measured with a Ubbelohde viscometer. A relationship between M-n and [eta] was obtained for ATPS. For 1.0 x 10(4) < M-n < 6.0 x 10(4), it was in accord with [eta](toluene,25 degreesC) = 5.26 X 10(-2) M-n(0.587).