Parthenium hysterophorus L. (Asteraceae) is a major weed in both cropped and non-crooped areas of India and many other countries. Considering the magnitude of problems caused by P. hysterophorus, its management is essential to prevent future complications. Leaf-feeding beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) has been proved as the most promising biocontrol agent of Parthenium in India and other countries. In the present study, sex ratio and sexual dimorphism of Z. bicolorata was studied using field samples collected during September month of 2013 to 2015 from different sites at Jabalpur (Madhya Pradesh, India). The male and female average sex ratio was observed as 1:1.50, 1:1.61 and 1:1.46 in 2013, 2014 and 2015, respectively. Sex ratio was significantly deviated towards the female. Females were distinctly larger and heavier in body size and abdominal width than the males. Further, experiments were conducted during rainy season of 2015 and 2016 to find out the effect of female dominated sex ratio, body weight and size by releasing of 7500 beetles/ha in two sex ratio viz. 1: 1 and 1: 1.60. Significant difference was recorded amongst these two sex ratios on density, height of plants, dry weight and number of flowers in Parthenium weed at 30 and 60 days after release of bioagent. Significantly higher effect of female dominated sex ratio (1:1.60) release was found in suppression of Parthenium. Therefore, for better and assured control, female dominated releases were recommended under biological control programme of Parthenium.