As a result of the critical importance of herbage quality and danger of poor mineral nutrition of forage legumes that affect livestock feeds in Nigeria, this investigation was conducted. The experiment entailed field trials at Samaru, Nigeria over three wet seasons to evaluate the response of mineral composition of lablab (Lablab purpureus L. Sweet) herbage to phosphorus application and cutting treatments. The treatments were composed of factorial combinations of four rates of phosphorus application (0, 12, 24 and 36 kg P ha-1), two cutting heights (10 and 20 cm) as the main plot and four cutting ages (6, 12, 18 weeks and at maturity) as the sub-plot a in split plot design with three replications. Cutting lablab to a 10 cm stubble produced significantly higher calcium and phosphorus concentrations in the dry herbage than cutting to 20 cm. The Ca:P ratio in the herbage increased as age of cutting increased but cutting height did not influence this parameter. A phosphorus application rate of 12 kg P ha-1 produced the highest ash concentration in lablab herbage under a 12-week cutting regime. However, the highest phosphorus concentration of lablab herbage was produced with a zero phosphorus application rate under a cutting height of 10 cm. Under the first herbage cut, ash content increased significantly with age of cutting. It is beneficial to feed lablab herbage to livestock before crop attains physiological maturity. The nutritive value of the herbage determines the most appropriate time to feed lablab herbage to livestock.