Objective: To evaluate the bioefficacy of α-cypermethrin impregnated into long lasting insecticide treated nets (LLITNs- INTERCEPTOR?) against main malaria vector, Anopheles stephensi (An. stephensi). Methods: The effectiveness of bed net impregnated withα-cypermethrin (INTERCEPTOR?) with washing was evaluated. The washing procedure and bioassay tests were carried out according to the WHO-recommended methods. Malaria vector, An. stephensi was exposed to impregnated bed net for three minutes and then mortality measured after 24 h recovery period. Knockdown was also measured according to the logarithmic times. Results:Result of cone bioassay method showed that bioefficacy ofα-cypermethrin decreased from 100%in unwashed to 15%in 20 washes. KT50 was measure as one minute in one wash and increased to 40 min in 20 washes. Discussion: Findings of this study provide guideline for malaria vector control authorities and people using pyrethroid-impregnated bed nets.