Limited research efforts have been made on cassava leaf usage for rearing eri-silkworm in relation to nitrogen fertilizer management. Hence, field and laboratory experiments were conducted at Jimma University (Ela-dale Site) during 2016 with the objective of determining the effect of nitrogen on leaf quality and identifying appropriate cassava variety for better leaf quality as a feed for Eri-silkworm performance. A 2x5 factorial experiment arranged in Randomized Complete Block Design (RCBD) with three replications was used. The treatments consisted of two cassava varieties (Kello and Qulle) and five levels of N (0,40,80,120 and 160 kg N ha^-1) as Urea. For the laboratory experiment, to rear eri-silkworm, cassava leaves harvested from the field experiment (10 plots) were arranged in Completely Randomized Design (CRD) with three replications and their effect on Eri-silkworm performance assessed in terms of larval, cocoon, and post cocoon traits. Data were collected on growth attributes, leaf proximate analysis of cassava, eri-silkworms larval, and cocoon and post cocoon traits. Variety and nitrogen had variable in both laboratory and fields experiment including biochemical composition of leaves. Variety Kello was found to be superior compared to Qulle by revealing a silkworm rearing performance indicators of hatchability (90.23%), fecundity (366.2 eggs/female), shorter larval duration (18.46 days), better larval weight (6.27 gm), survival rate (92.66%), cocoon weight (3.44 gm), single shell weight (0.47 gm), pupal weight (2.96 gm) and effective rate of rearing (89%). Application of 160 kg N ha^-1 gave highest hatchability (93.85%), fecundity (384.83 eggs per female), larval weight (6.5 gm), shell weight (0.51 gm), cocoon weight (3.66 gm), pupal weight (3.15 gm) and shortest larval duration (17.333 days). In terms of biochemical composition, kello leaves had higher moisture content (0.438%), ash (18.541%) and crude fat (16.69%). Higher crude fiber (16.248%) and total carbohydrate (27.234%) were obtained from Qulle variety. 160 kg N ha^-1 gave the highest moisture (0.467%) and the lowest crude fiber (14.123% ). The highest leaf nitrogen content (4.802%) and crude protein (30.012%) was gained from the combination of kello and 160 kg N ha^-1. In conclusion, variety Kello and 160 kg N ha^-1 can be used for higher leaf yield, leaf quality and cocoon yield.