The aim of this study was to determine the in vitro anticancer effects of hypocrellin B (HB) in SiHa human cervical cancer cells by MTT, flow cytometry and RT-PCR assay, as well as to explain the mechanism of this effect through the caspases expression changes by HB. The SiHa cells were treated with 1 and 2 μg/mL HB and meanwhile these cells were also irradiated by the light (LED: light-emitting diodes). The results showed that HB could reduce the growth of SiHa cells, and LED irradiation increased the inhibitory effects. Treatment of 2 μg/mL HB could induce apoptosis in cancer cells (sub-G1 DNA content) at 32.8%, and after LED irradiation, the apoptotic cancer cells raised to 46.8%. The 2 μg/mL HB+LED treated SiHa cells had the highest caspase-3 activity, with 4.61 ± 0.21-fold to control cells. Both LED and 2 μg/mL hypocrellin treated SiHa cells had the strongest caspase-3, caspase-8, caspase-9, Bax, Fas/FasL, TRAIL, DR4, DR5, ROS and weakest Bcl-2, Bcl-xL mRNA expressions. These results proved that HB had a good in vitro anticancer effect, and LED irradiation could raise its anticancer effect, this effect might be derived from the influence of caspases and caspases related gene expressions by HB. HB could be used as a good cancer treatment drug.