Abstarct: The aim of this experiment was to study the effect of ultrasonic waves and nitroxin biological fertilizer on growth and yield of cowpea. The experimental design was randomized complete blocks design with three replications. Treatments consisted of factorial arrangement of ultrasonic waves, in five levels of zero exposure (F1), 2 (F2), 4 (F3), 6 (F4) and 8 minutes (F5) and three levels of nitroxin biological fertilizer inoculation, including control (B1), recommended amount of inoculation (B2) and twice recommended inoculation (B3). Results showed that inoculation of growth stimulating bacteria (Azotobacter and Azospirillum) significantly increased plant height, number of node, number of pod and grain, grain and biological yield and chlorophyll content of leaves and protein percentage, nitrogen and grain oil as compared to controls. Ultrasonic waves also increased plant height, distance of first pod from soil surface, number of nodes, weight of 100 grains, dry weight of stem, grain oil content, chlorophyll content of leaves, and biological yield. Also the interaction of nitroxin biological fertilizer and ultrasonic waves was significant for the distance of first pod from soil surface, number of nodes, dry weight, pods, leaves, stem and chlorophyll content of leaves. It was concluded that applying nitroxin fertilizer and also, 4 and 6 minutes exposure to ultrasonic waves are useful to improve growth and yield of cowpea.