Mustard (Brassica juncea L.) is an important oil seed crop in India. Water is most often the limiting factor for mustard production and its optimum use is essential for higher yields. Evapotranspiration is an integral part of the overall water requirement' problem of any crop and its determination becomes both desirable and inevitable for better acquisition of the knowledge of water utilization by the crop. A field experiment with four depths of irrigation (T1-irrigation with 30 mm of water, Ig-irrigation with 45 mm of water, I o-irr igat ion with 60 mm of water and I4- irrigation with 75 mm of water) with four irrigations using sprinkler system each at a fixed interval was laid out in completely randomized block design during the rabi season of the year 1992-93. The results revealed that, the yield differences due to irrigation treatments were found to be non-significant. The data indicated that none of the irrigation treatments had any significant effect on the yield and yield attributing characters. The leaf area index (LAI) value was not sensitive to the different depths of moisture levels. Regression analysis between LAI and days after sowing (DAS) indicated that quadratic regression equation could fit well to predict LAI from DAS. Study on evapotranspiration indicated that total ovapotranspiration increased with increase in amount of water applied. Accumulated Stress Degree Days (SDD) values decreased with increase in amount of water applied. Correlation studies between dry matter production and intercepted photosynthetically active radiation (IPAR) indicated high positive correlations. Studies on intercepted photosynthetically active radiation (IPAR) indicated that IPAR use efficiencies ranged from 2.44 g MJ-1 in I2 treatment to 2.55 g MJ-1 in I1 treatment. The extinction co-efficient (K) calculated by using incident photosynthetically active radiation (PAR) and transmitted PAR showed a value of 0.87.