Gold nanoparticles are considered of great importance compared to other noble metal nanoparticles and its wide range of applications like pharmaceutics, therapeutics and diagnostics etc. During the past decade, phytosynthesized gold nanoparticles (AuNPs) are more focused in in vitro and in vivo study. The present study was focused on the gold chloride and phytosynthesized gold nanoparticles from aqueous leaf extract of Cassia roxburghii and their toxic effects on African green monkey normal kidney Vero cell line and three different cancer cell lines such as HepG2, MCF7 and HeLa. Phytosynthesized AuNPs were characterized by HRTEM, EDX, XRD and FTIR analysis. The particles size range of 25-35nm was confirmed by HRTEM. The elemental gold and the crystalline nature of AuNPs were confirmed by EDX and XRD, respectively. The reduction of functional groups was confirmed by FTIR. In in vitro study, the IC50 of HepG2 cells was found to be 30μg/ml compared to other cell lines, HeLa and MCF7 cell line showing IC50 of 50μg/ml and normal Vero cell line also nontoxic up to 75μg/ml confirmed by MTT assay. Further, apoptosis in HepG2 was analyzed by fluorescence microscope and DNA fragmentation was observed in HepG2 treated cells. These results suggested that phytosynthesized AuNPs of C. roxburghii extract clearly limited toxic on normal cells but toxic in cancer cells.