The first phase transfer-catalysed direct γ-substitution of Morita-Baylis-Hillman carbonates of isatins with 3-substituted oxindoles has been developed, which affords 3-alkenyl-oxindole ring-fused 3,3'-disubstituted oxindoles in up to 83% yield under mild reaction conditions. Furthermore, their biological activity has been preliminarily demonstrated by in vitro evaluation against human prostate cancer cells PC-3 and human leukemia cells K562, using MTT-based assays with the commercially available standard drug Cisplatin as a positive control. Gratifyingly, compounds 3aa, 3ba and 3ca exhibited comparable in vitro inhibitory activities against human prostate cancer cells (PC-3) to Cisplatin. What's more, 3ba also had a good inhibition ability against human leukemia cells K562. These results indicate that 3-alkenyl-oxindole ring-fused 3,3'-disubstituted oxindole analogs may be potential lead compounds for further biological screening.