Tumour cells maintain a local hypoxic and acidic microenvironment which plays a crucial role in cancer progression and drug resistance. Urease is a metallohydrolases that catalyses the hydrolysis of urea into ammonia and carbon dioxide, causing an abrupt increase of pH. This enzymatic activity can be employed to target the acidic tumour microenvironment. In this study, we present the anticancer activities of urease mimetic cobalt (III) complexes on A549 cells. The cells were treated with different doses of cobalt (III) complexes to observe the cytotoxicity. The change in cellular morphology was observed using an inverted microscope. The cell death induced by these complexes was analysed through ATP proliferation, LDH release and caspase 3/7 activity. The effect of extracellular alkalinization by the cobalt (III) complexes on the efficacy of the weakly basic drug, doxorubicin (dox) was also evaluated. This combination therapy of dox with cobalt (III) complexes resulted in enhanced apoptosis in A549 cells, as evidenced by elevated caspase 3/7 activity in treated groups. The study confirms the urease mimicking anticancer activity of cobalt (III) complexes by neutralizing the tumour microenvironment. This study will motivate the applications of transition metal-based enzyme mimics in targeting the tumour microenvironment for effective anticancer treatments.