A series of thirteen 5H-dibenzo [b,e][1,4]diazepin-11(10H)-one structural derivatives has been synthesized and evaluated for anti-proliferative activity against five human cancer cell lines. Compound 9a exhibited potent tumour growth inhibition in all cell lines with IC50 values in the range of 0.71-7.29 μM. Experiments on lung (A549) and breast (MDAMB-231) cancer cell lines to investigate the mechanisms of growth inhibition and apoptosis inducing effects of 9a showed that it arrested both cancer cell lines in the G2/M phase of cell cycle in a dose dependent manner. Hoechst staining analysis revealed that 9a inhibited tumour cell proliferation through apoptosis induction. Additionally, the mitochondrial membrane potential (ΔΨm) was affected and the levels of reactive oxygen species (ROS) were raised. The simple synthetic preparation and their biological properties make these dibenzodiazepinone-triazole scaffolds promising new entities for the development of cancer therapeutics.