An experiment was carried out to evaluate the biochemical response of mustard to naphthalene acetic acid (NAA). Six levels of NAA such as G0 (no NAA or control), G1 (30 ppm ha^-1), G2 (50 ppm ha^-1), G3 (70 ppm ha^-1), G4 (90 ppm ha^-1) and G5 (110 ppm ha^-1) were tested. The leaf chlorophyll content was recorded at 30, 40, 50 and 60 days after emergence (DAE). The NAA significantly influenced the biochemical property. The highest chlorophyll level was recorded in 70 ppm NAA ha^-1 at 50 DAE. At 45 DAE, the highest nitrogen content was noted in 70 ppm NAA ha^-1. The 70 ppm NAA ha^-1 also showed the maximum oil content. The minimum acid value, peroxide and saponification values were found in 70 ppm NAA ha^-1. The maximum iodine value was observed in 70 ppm NAA ha^-1. Nonessential chemicals likes stearic, palmitic and erucic acid were augmented in the mustard with a decrease in the NAA level while necessary fatty acids were highest in 70 ppm NAA ha^-1. It is suggested that 70 ppm NAA ha^-1 can be used to grow quality mustard plants.