Plant growth regulators (PGRs) are used in cotton production to optimize yield and quality and even suppressing excess growth whenever necessary. Experiments were conducted in 2017 at Cotton Seed Multiplication, Training and Research Farm, Sreepur, Bangladesh to study the response of lint index of cotton to different plant spacings, concentration and time of application of mepiquat chloride (MC) growth regulator. Plant spacings like 45 cm × 30 cm, 60 cm × 30 cm and 75 cm × 30 cm; MC spray @ 1.0, 2.0, 3.0 and 4.0 ml  L-1  water at 25, 50 and 75 DAE for each concentration along with water spray as control, were the treatment variables. Lint index (LI) of cotton was maximum (8.74 g) at spacing 60 cm × 30 cm and the lowest lint index (7.71 g) was recorded from spacing 45 cm × 30 cm. In respect of mepiquat chloride (MC), the highest lint index (9.99 g) was from 3 ml MC L-1 water at 25 DAE and the lowest (7.04 g) with 4 ml MC L-1 water at 25 DAE. Considering treatment combination, LI observed highest (10.30 g) at 4 ml MC L-1 water at 50 DAE with 45 cm × 30 cm spacing and marked lowest (7.00 g) at 4 ml MC L-1 water at 25 DAE with    75 cm × 30 cm spacing treatment combinations.

Key words: Plant spacing, growth regulator, time of foliar, lint index, cotton