A convenient and simple radical cation cyclisation of 3,5-dimethoxystilbene was developed using the commercially available FeCl3 under mild condition. It enabled the construction of a new class of indolostilbenes (i.e., indole-stilbene hybrid). Various parameters were investigated to obtain better yields (more than 42%) compared with the previously reported. The synthesised indolostilbenes were characterised, and their mechanism of formation was discussed. The synthesised compounds were submitted for biological assay on NG108-15 cell viability and H2O2-induced cytotoxicity. The result showed that two indolostilbenes have promising protective activity against H2O2.