The rate at which tomato fruits ripe was investigated via the biosynthesis of lycopene in two tomato varieties under the conditions of field and ambient temperature ripening. Results showed that the biosynthesis of lycopene follows a first-order kinetics in both varieties with calculated rate constants of 1.2×10-2 and 1.4×10-2 d-1 for Ibadan local and Roma types respectively under the field ripening; and 2.1×10-2 and 5.3×10-2 d-1 for Ibadan local and Roma types respectively at the ambient temperature ripening. The formation of β-carotene follows zero-order kinetics in both varieties under the field ripening after 8 days (Roma type) and 10 days (Ibadan-local type), with respective calculated rate constants of 43.81 and 54.7 ppm d-1. No simple order was obtained for the formation of β- carotene at the ambient temperature ripening. The empirical rate law for the lycopene biosynthesis under the field ripening suggests the expression: 0 k t k 1[GGPP]e k dt d[Lycopene ] = − 1 − where GGPP is geranyl geranyl diphosphate.