The effect of the anti-moulting agent diflubenzuron were studied against the nymphal  instars Berseem Grasshopper Euprepocnemis Plorans Plorans (Charp) .The tested rates of 40 / 20 / 10 gm. a.i /fed. were sprayed on alfa alfa Medicage sativa. Groups of 4^th instar nymphs were continuously fed on the treated alfa alfa to the next moult to 5^th instar. This treatment induced low percentages of failure in ecdysis to the 5^th instar. The high percentages of failure in ecdysis and mortality were obtained within the 5^th instar especially during metamorphosis to the adult stage . The prolonged duration of the treated 4^th instar and the decreasing of the body weight of the resulting 5^th nymphs and the corresponding adults, specially in the treatment with the high rate (40 gm.a.i/fed.) suggested that. Diflubenzuron was a rate dependent against grass hopper E. Plorans Plorans, and this compound could be a good preventive control tool against the nymphal instars of this insect pest in their breeding sites.