Abstract: The effect of nutrition on different host plants (cabbage, castor bean and cotton) on midgut redox potentional (Eh), midgut pH and digestive enzymes of the fourth larval instar of Agrotis ipsilon was studied. The results showed that all larvae had strongly alkaline midguts pH ranging from 9-9.75. There were no significant differences between midgut pH of larvae fed for 24 h or that fed for 7 days, effect different host plants, reflecting the rapidity by which the larvae adjust their midgut pH. On the contrary, plant species had a significant effect on mid gut Eh. Conditions in all guts were oxidizing ranging from +171 to +250 mV i.e., all tested midguts Eh were positive. The results also revealed that continuous feeding on host, plants for 7 days significantly lowered the oxidizing state of gut, except cabbage, as compared to those larvae fed for 24 h. Each host plant had own specific effect on protease, lipase and invertase. However lipase was the least enzyme that affected. The study clarifies the effect of host plants on midgut physicochemistry which mid gut affect digestion and gut physiology, ultimately affecting the normal growth of the pest.