The American cockroach, Periplaneta americana (L.) is considered one of the most important medical and veterinary insects among 3500 species in the world, control methods have been developed for these insects using some plant extracts and green nanoparticles of some medical plants such as rosemary (Rosmarinus officinalis L.). The present work was conducted at the Economic Entomology & Agricultural Zoology Department, Faculty of Agriculture, Menoufia University during 2020-2021 under laboratory conditions. The objective of the present study was to investigate the toxicity and biochemical effects of the ethanol extract and nanoparticles (NPS) of rosemary on the nymphs and adults of the American cockroach. The results demonstrated that the LC50 values of nanoparticles of rosemary extract were the most toxic for the two stages than the rosemary ethanol extract. LC50 values for nanoparticles extract were 118.22 and 112.33 ppm when contact and feeding technique were applied for nymphs, respectively, while for adults were 127.41 and 121.12 ppm when contact and feeding technique were applied, respectively. Additionally, these compounds had biochemical effects, which generally led to a decrease in the total content of protein and an increase in the total content of carbohydrates and lipids. Moreover, the activity of the acetylcholinesterase enzyme was increased. In general, the treatment with feeding was more effective than contact treatment.