Bacillus sphaericus ts-Dl290 was characterized by SDS-PAGE produced by the mutant at $30^{circ}C$ and $42^{circ}C$. The total amount of proteins produced by the mutant at $42^{circ}C$ decreased to one-fifth of those at $30^{circ}C$; however, when the culture was shifted down from $42^{circ}C$ after 4 to $30^{circ}C$, the total amount of protein decreased to one-third and the 221 kd protein did not appear, but the 155 kd appeared remarkably. When the mutant and the wild type strain were cultured in the media containing 80$mu g$ per ml of chloramphenicol at $42^{circ}C$, the wild type strain synthesized half amounts of the total proteins than those at $30^{circ}C$, and the mutant produced one-tenth of the total protein amounts. When the both strains were cultured in the media containing chloramphenicol, the 155 kd protein was produced was produced in lesser amounts than those without chloramphenicol. The 150 kd protein showed lethal activity to Culex pipiens 3rd instar larvae.