The effects of nitrogen nutrition and day temperature on composition, color and nitrate in VF–145 tomatoes were investigated in growth chambers kept at 20, 25, 30 and 35°C respectively during the days for 14 hr, and at 20° C during the nights for 10 hr. Nitrogen fertilizer application was altered in half the pots in each chamber by supplying them with half‐strength −N Hoagland's #1 solution during the fruit growth period. Tomatoes from fertilized plants (+N) were slightly higher in titratable acidity but lower in solids content than those from the −N plants. Fruits ripening at high day temperature were poor in color while those ripening at below 30°C were more attractive in color. The total, amino, ammonium and nitrate nitrogen contents of the tomato fruits were higher in the +N series than those of –N series. Tomatoes from plants receiving +N treatments contained more nitrate than those receiving −N treatments. Day temperature greatly affected the nitrate content in the tomatoes. In the +N series the nitrate content of the tomatoes decreased from 72.9 ppm to 0.37 ppm as the day temperature increased from 20: to 35°C. In the −N series, the nitrate content ranged from 0.35–1.15 ppm. Accumulation of nitrates in tomatoes appears to be related to the level of nitrate in the nutrient solution and the day temperature. Low day temperature results in accumulation of nitrate because of the low nitrate