Gold nanoparticles (AuNPs) is the most excellent anticancer theranostic nanoparticles synthesized through efficient, simple and green synthesis method using extracts of Trichosanthes kirilowii, extensively characterized by UV-spectroscopy, FT-IR and TEM techniques. The AuNPs, synthesized by means of T. kirilowii extracts identified that nanoparticles were $50 nm in size, which is an admirable nano dimension attained by green synthesis. In agreement with the outcome of microscopic cellular morphological observations, MTT assay showed effective, selective, anticarcinogenic effect of AuNPs on HCT-116 cells in a dose-dependent manner. The AuNPs significantly enhance ROS generation, cause mitochondrial membrane damage and induce morphological changes using AO/EtBr staining assay. Furthermore, AuNPs treatment induces G0/G1 phase cell-cycle arrest in HCT-116 cells. Also, AuNPs treatment activates caspase expression and downregulates the anti-apoptotic expression in HCT-116 cells. Our results point out that the phytoconsituents isolated from T. kirilowii can act as appropriate reducing and stabilizing agents in the properties of AuNPs; hereby, it leads to the green synthesis of an anti-carcinogenic agent with highly efficient potential for cancer treatment.