The values of crack growth rate for styrene-butadiene copolymer (SBR) and acrylonitrile-butadiene copolymer (NBR) under dynamic tearing condition were measured in both dry and swollen conditions. For swollen samples, tearing energy was adjusted by a simple geometrical factor lambda(delta)(2) (where lambda(s) is the linear swelling ratio), in order to take into account the reduction in number of molecular chains per unit fracture plane. The crack growth rate of a swollen elastomer was observed to be significantly increased over the measured range of tearing energy compared to that of an unswollen elastomer. The effects of the type of elastomer, degree of swelling, and crosslinking structure on fatigue crack behaviour of swollen elastomers are discussed.