An evaluation of six dietary protein to energy (P/E) ratios was conducted in the early juveniles of ornate spiny lobster (Panulirus ornatus) by investigating the effects on physiology, digestive enzyme activities, body composition and amino acid profiles. Lobster juveniles (0.25 ± 0.01 g) were individually kept in aquaria and fed 6 isoenergetic formulated diets consisting of three protein levels (450, 500 and 550 g kg− 1) and three lipid levels (7, 9 and 13 g kg− 1) having P/E ratios of 21, 22, 23, 24, 25 and 26 mg MJ− 1. After 8 weeks of feeding, the dietary P/E ratio influenced the specific growth rates, while survival, moult increment, moulting rate and moult interval were not affected by any dietary P/E ratios. The dietary protein levels had stronger influence on the specific growth rate whereas dietary lipid levels affected the length increments. The dietary P/E ratio also influenced the protease, lipase, super oxidase dismutase activities and the body composition of spiny lobster juveniles. Both protein and lipid in the whole body of the juveniles reflected the dietary composition. The total quantity of non-essential amino acids was higher than essential amino acids in the formulated diet and also in the body of juvenile lobsters. Results clearly indicated that 55% and 9% dietary protein and lipids, respectively with 26.6 g CP MJ− 1 can yield the maximum growth and digestive enzyme activities.