Losses in tomato (Solanum lycopersicum) production in Zimbabwe have been attributed to Pythium spp induced damping–off. Current research trends in seedling production suggest that Trichoderma harzianum has a positive effect on nursery diseases. T. harzianum uses a variety of mechanisms to colonise various ecological niches. Different plant varieties have different affinity levels for T. harzianum. In this research an evaluation was done on the effect of four different rates of T. harzianum (0cfu/ml, 105cfu/ml, 106cfu/ml and 107cfu/ml) and four tomato varieties namely Floradade, Money-maker, Rodade and Star 9064 in controlling Pythium spp damping-off. A 4x4 factorial experiment was laid in a completely randomized design with three replicates. Four different tomato varieties were primed with T. harzianum suspension for 24 hours and then sown in float trays according to the experimental design. Data was collected on emergence percentage, growth (number of true leaves and plant height); damping-off incidence and severity and dry weight. There was a significant interaction (P=0.001) between T. harzianum and variety on all parameters. T. harzianum 106cfu/ml and T. harzianum 107cfu/ml had no disease incidence and severity recorded on all tomato varieties. Emergence percentage, number of true leaves and dry weight increased on Money-maker and Star 9064 with an increase in T. harzianum rate. T. harzianum did not induce an increase on Rodade plant height. This study was carried out in the view of the use of T. harzianum as a bio-control strategy for Pythium-induced damping-off on tomato seedlings.