In this article we evaluate the effects of ultrasound radiation and its causes on the rate of injured peripheral nerve regeneration by crushing the sciatic nerve of rats with hemostatic forceps. The rats were divided into three test and one control groups. The test groups were radiated using three different types of ultrasound parameters while the control group just received sham expose. The amount of nerve regeneration was measured via functional test by extracting sciatic functional index from rats paw prints. The results showed that one of the test group parameters had the best functional results compared to other groups. Obtaining this outcome, the investigations continued by 50 rats with crushed sciatic nerve. These rats again divided into two test and control groups while for the test group the best parameters were assigned. In different time intervals compound muscle action potential wave was recorded from five rats of each group. Then their sciatic nerves were extracted to measure the amount of ciliary neurotropic factor gene expression by real time polymerase chain reaction. Crush injury sets the sciatic functional index to about -90 and compound muscle action potential to 6.8 mV in both control and test groups. After the period of treatment with ultrasound, the sciatic functional index reached the value of -25 in control group and -10 in test group and compound muscle action potential value reached 11 in control and 18 in test group. The results of electrophysiological tests confirmed the results of functional tests. At the end of the second, third and fourth weeks, the outcomes of real time polymerase chain reaction showed that the expression of ciliary neurotropic factor gene in test group was higher than control group as well as the amount in test group was approximately 11, 2 and 6 times higher than test group in corresponding weeks. Hence we can conclude that increase in the expression of ciliary neurotropic factor gene, as a nerve growth factor, following ultrasound radiation, can be considered as the reason of the effect of ultrasound on the rate of injured nerve regeneration.