The extent of solubility of Li+ in monoclinic CuO and its effect on the crystal structure and electrical behaviour have been studied employing different experimental techniques. It is found that (i) the extent of lithium incorporation in CuO is limited to ≤ 25at%, (ii) the defect compounds, Cu1-xLixO1-δ, are formed without altering the crystal structure and (iii) the resistivity decreases with increase in Li concentration. Further, it is observed that these compounds continue to exhibit semiconducting ( dρ{variant} dT < 0) behaviour. © 1994.