Laboratory bioassays were carried out to evaluate the insecticidal efficacy of two Iranian deposits of diatomaceous earths (DEs) and a commercial formulation, SilicoSec(R), against adult confused flour beetle (Tribolium confusum Jacquelin du Val). The Iranian DEs were dried and sieved to get particle sizes of 0-149, 74-149, 0-74 ${mu}m$, and 0-37 ${mu}m$. First, DE samples were applied at the four concentration levels of 500, 1000, 1500 and 2000 ppm and each concentration was replicated four times. Tests were carried out at $27{pm}1^{circ}C$ and $55{pm}5%$ r.h. in continuous darkness. The beetle mortality was counted at 2, 7, and 14 days after exposure. Moreover, another experiment was conducted to estimate the $LC_{50}$ values of the DEs. For the first experiment, adult beetle mortality exceeded 51% when exposed for 2 d to 2000 ppm of SilicoSec(R). Complete mortality was recorded at each concentration of SilicoSec(R) at an exposure longer than 7 days except for 500 ppm; while mortalities of T. confusum at 2000 ppm of Maragheh and Mamaghan samples with the 0-149 ${mu}m$ particle size were 40.62% and 85.41%, respectively. Mortality of T. confusum was influenced by concentration and time of exposure to the DEs. SilicoSec(R) was the most effective DE followed by Mamaghan samples. The Maragheh samples were the least effective. In addition, in most cases fractions with smaller particles were more effective than larger ones. More experiments are necessary to process natural DEs and make them commercially exploitable.