Environmental pollutants, like pesticides, have been destructive on different aspects of life. Silkworm, as a beneficial insect, is no exception to this matter. Due to this, many problems have appeared in sericulture because of pesticide applications to cultivations, especially when mulberry trees grow next to cultivated plants. Many studies that have focused on the effect of insecticides on B. mori deal with toxicity, retardation of development and growth, fecundity, mortality, food utilization and economic parameters (Vassarmidaki et al., 2000). However, between these studies a few documents focused on the effect of fungicide residue on silkworm growth and performances (Dutta et al., 2003). Sik et al (1976) reported that more than 1.4% of yield reduction in sericulture is due to side effect of pesticide application. 49.4% was due to the application of different pesticides in rice filed, 21.2% in fruit garden and 12.3% in olericulture. Therefore, the present investigation deals effects of long term application of systemic insecticide, Oxydemeton-methyl(metasystox R) on some biological performance of silkworm. Because metasystox has just recently used to against of mulberry thrips in sericulture and it is necessary to study different side effects of this insecticide on silkworm.