Effects of topical application of 100, 200 and 300ng/$mell$ of 3-indole butyric acid (3IBA) on larval parameters were studied in polyvoltine Pure Mysore breed of B. mori. Each concentration was administered independently, at 36h to III, IV ＆ V instars, at 48h to IV ＆ V instars, and at 72h to V instar larvae. Of the various dosages used, the repeated applications of loons of 3-IBA at 36h to III, IV ＆ V instars resulted in a significant increase in larval weight, silk gland weight, cocoon shell weight and fecundity and a significant decrease in larval duration and cocooning percentage when compared with the corresponding parameters of the untreated controls.