The effect of chronic radiation, 100, 1000 and 4000 times exceeding the natural background radiation, on embryogenesis of silkworm, Bombyx mori has been investigated. It is shown that low level ionizing radiation shortens by several hours the period of embryogenesis while the larva mass increases as the development proceeds. A single preincubational exposure of silkworm eggs to a dose of 2 Gy increases the mass of larvae as well as the cocoon shell weight, silk-bearing and the raw silk production.