In this study, deltamethrin (K-Othrine Ò), a synthetic pyrethroid derivative, was investigated regarding to its effects on humoral immunity and some blood parameters. Total 60 White mice used; which were separated into 3 groups, each of them consisted of 20 animals. Group 1 was a control; Group 2 and 3 were treated as experimental groups. Normal feed was given to Group 1. While Group 2 received 7.5 mg/kg.bw/day deltamethrin, Group 3 had 30 mg/kg.bw/day deltamethrin in their feed during 30 days. As a result, deltamethrin suppressed immune system in term of subacute but it had no effect on blood parameters except leukocyte.