Abstract: A field experiment was conducted to investigate the effect of potassium and its time of application on yield and quality of tomato variety, Nagina. Treatments included three potassium levels i.e. 60, 90 and 120 kg ha-1 and two application timings: at transplanting as single dose, and half at transplanting + half at 40 days after transplanting in two splits, were applied along with a control (0 kg ha-1 K). Potassium application @ 60 kg ha-1 either applied in single or in two splits, significantly increased the yield and improved the quality parameters of tomato over control while higher levels of K (90 and 120 kg ha-1) did not show further significant increase in the yield and quality subsequently. Ascorbic acid remained unaffected. Results revealed that time of application/splitting of K did not affect the yield and quality. The highest yield (23.3 t ha-1), firmness (8.32 kg), fruit weight (83.24 g fruit-1 ), total invert sugars (4.11 % ), dry matter (6.33 %) and mineral matter (1.95 %) were recorded with the application of 120 kg ha-1 potassium at transplanting while the highest values of acidity (0.81%) , TSS (7.03 %) and ascorbic acid (30.33 mg 100 g-1) were observed in treatment where potassium was applied @ 60 kg ha-1 in two splits. Minimum yield (17.2 t ha-1), firmness (6.35 kg), fruit weight (68.11 g/fruit), mineral matter (1.80 %), dry matter (5.26 %), acidity (0.61 %), ascorbic acid (21.79 mg 100g-1), TSS (6.60 %) and total invert sugars (3.85 %) were found in control.