The extract of Caesalpinia pulcherrima (C. pulcherrima) is one of the common herbal drugs which have a key role in treating pyretic, microbial infections, cancer and for several other traditional systems of treatment. In our present work, we demonstrate the bioactivities of extracts and cytotoxicity of synthesized silver nanoparticles on HCT116 cell line. The qualitative phytochemical tests indicated the presence of some adequately required metabolites as follows; the total phenolic content in the aqueous extract contains a higher amount of phenolic compounds (815 ± 0.013 μgmg−1). The DPPH quenching activity of the aqueous extract showed an IC50 value of 18.7 μg which was equivalent to the IC50 value of ascorbic acid (15 μg) and methanolic extract (51 μg). The test extracts showed 4.6% haemolytic activity that attributes to its protective and non-toxic nature. The zone of inhibition of aqueous extract shown against the growth of E.coli was 25 mm. Further, silver nanoparticles synthesis was carried out with the extract and was characterized by X-ray diffraction, particle size analyzer, zeta potential, TEM- EDAX and UV spectroscopy. XRD analysis indicated the crystalline nature of silver nanoparticles with a face-centered cubic structure. The data obtained from the particle size analyzer demonstrated as 155.4 nm of the size of the synthesized silver nanoparticles. The values of zeta potential (−23.4 mV) revealed that the nanoparticles were extremely stable in colloidal form. SEM indicated the spherical shape of silver nanoparticles with the size range between 177.9 nm to 251.1 nm. Beside the efficient bioactivities, the synthesized C. pulcherrima silver nanoparticles showed significant cytotoxicity effect of 77.5% on a human colon cancer cell line. Therefore, along with antioxidant, antibacterial, haemolytic activity; C. pulcherrima also accomplished satisfactory cytotoxic property in anticancer mechanism as proven by this study. © 2019 Elsevier B.V.