Plant growth regulators (PGRs) are used in cotton production to optimize yield and quality and even suppressing excess growth whenever necessary. An experiment was carried out during August, 2016 to January, 2017 at Cotton Seed Multiplication, Training and Research Farm, Sreepur, Bangladesh to evaluate the response of seed cotton yield to different plant spacing and time of application of mepiquat chloride (MC) growth regulator. Five plant spacing like 60 cm × 30 cm, 60 cm × 40 cm, 75 cm × 30 cm, 75 cm × 40 cm and 90 cm × 45 cm; MC spray @ 1.0 ml L-1 water at 25, 50, 75, 100 and 125 DAE along with water spray as control were considered as the treatments of the experiment. Narrow plant spacing i.e. plant spacing of 60 cm × 30 cm showed the highest values of maximum seed cotton yield (4.2 t ha-1). In case of MC application, maximum seed cotton (2.62 t ha-1) was noted from 1.0 ml MC L-1 water sprayed at 25 DAE. So, foliar application of mepiquat chloride @ 1 ml L-1 water at 25 DAE along with plant spacing of 60 cm x 30 cm can be practiced for profitable cotton production at Sreepur, Gazipur areas of Bangladesh.

Key words: MC, foliar application, spacing, seed cotton, yield.