Abstract: Considering the role of phenolics in plant defensive strategies, some cotton varieties with varied degree of insect resistance and susceptibility were analyzed through HPLC for their phenolic content. Out of 15 major peaks, 9 were identified as galic acid, protochatechuic acid, chlorogenic acid, p.hydroxy benzoic acid, syringic acid,p.coumaric acid, gentisic acid, benzoic acid and ferulic acid. Major quantitative differences were seen for syringic and ferulic acids being significantly higher in resistant variety Ravi and present only in traces in more susceptible varieties, NIAB-26N and S-12. Individual effect of some phenolic acids on growth and survival of cotton bollworm also showed extreme retardation of larval weight (99.42% to 99.71%),100% mortality( in 1st week) and no pupation in diet incorporated with these two acids syringic and ferulic acids. p-hydroxy benzoate, chlorogenic, sinapic and cinnamic acids showed 45 to 80 % retarded weights, 16 to 33% mortality in 1st week and 61 to 94% mortality in 2nd week and 5 to 40% pupation with 2 to 4 days delay.