Groundnut (Arachis hypogaea L.) is a self-pollinated, auto-tetraploid legume crop with 2n=40 chromosomes and belongs to the family Fabaceae. Mepiquat chloride (MC) is an important growth retardant inhibits vegetative growth and accelerates the development of reproductive parts by reducing plant height, thereby decreasing the distance between the source and sink, resulting in better translocation of photosynthetic into developing pods, which is expected to improve groundnut harvest index. Hence the present study, was conducted on SG99 to test the efficacy of growth retardant mepiquat chloride at five concentrations (100,300,500,700 and 900 ppm) keeping check as control. Single foliar spray of mepiquat chloride was given at 40, 60 and 80 DAS. The growth retardant, mepiquat chloride @700ppm significantly reduced days to initiation of flowering, 50%, completion flowering for 4.0 days whereas SPAD value increased by 4.32%. Similarly, Physiological data recorded at 60 and 90 DAS revealed that plant height, root length, root weight was decreased with mepiquat chloride @700 ppm. However, number of branches, nodules number, and nodules weight, dry weight of root, leaves and shoot were more with mepiquat chloride @700 ppm over control. Hence, our results revealed the effective concentration was 700 ppm of the growth retardant.