The current study was carried out at the Experimental Farm of Sakha Agricultural Research Station, Egypt during two successive seasons 2014/15 and 2015/16 to estimate percentage of parasitism by Opius nitidulator (Nees) on larvae of Pegomyia mixta Vill. infested sugar beet, chard weed, Beta vulgaris var Cicla, L. and common lambsquarter weed, Chenopodium album L. as dominant weed plants in sugar beet fields. They belong to Family Chenopodiaceae. The percentages of parasitism ranged between 1.30 to 100, 7.41 to 97.14 and 0.00 to 100% on sugar beet plants, chard weed and common lambsquarter weeds in 2014/15 season, respectively. While, in the second season2015/16 were  5.00 to 63.00, 13.00 to 95.24 and 0.00 to 87.50% on sugar beet plants, chard weed and common lambsquarter weed, respectively. The average rates of parasitism were 25.00, 29.50 and 36.00% on sugar beet plants, chard weed and common lambsquarter weed, in 2014/2015 season, respectively. Meanwhile, in the second season 2015/16 were 27.22, 36.20 and 39.24% on sugar beet plants, chard and common lambsquarter weed, respectively. These results show that the importance of chard and common lambsquarter weeds which found around borders or between fields (on dikes, slippers and furrows) in enhancing the numbers of the parasitoid, O. nitidulator in sugar beet fields against P. mixta.