A 12-m tractor mounted boom sprayer was modified and developed considering the various components of the existing boom sprayer. The modifications were done in the boom sprayer for stability and new folding arrangement and further it was fabricated. The hydraulic boom sprayer was tested using the spray scanner and droplet analyzer in the laboratory for cotton crop to study effect of nozzle discharge rates (viz., 0.45, 0.70, 0.90 and 1.35 l/min) and nozzle pressures (viz., 275.8, 413.7, 551.6 and 689.5 kPa) on spray uniformity. From the study it was found that nozzle discharge rate of 0.9 l/min and nozzle pressure of 689.5 kPa produced more uniform spray. The liquid distribution under the boom sprayer was within the ±20 per cent of total mean value, which was within the limits as per standards. Droplet size (VMD), droplet density (DD) and uniformity coefficient (UC) of the boom sprayer ranged from 155.44 to 181.55 µm, 17 to 29 drops/cm2 and 0.99 to 1.23 respectively.