This study has been conducted to determine effect of ankle joint inversion trauma on common peroneal nerve motor conduction velocity (MCV). Twenty patients (8 males and 12 females) who were 30 to 45 years of age (X=33.75+1.15) participated in this study. They received the same medical care and manual tests for the inversion trauma. The involved lower limbs were considered the experimental group, while the normal contralateral lower limbs were considered the control group for all the twenty patients. Measurements of the MCV were carried out 10 days post trauma as a first record and one month post trauma as a second record for the both groups. Data collected for the first record showed that averages of MCV (m/sec), were 29.50+2.14 and 42.45+3.08 for the experimental and control groups respectively. While data collected for the second record showed that averages of MCV (m/sec), were 31.02+2.25 and 42.80+3.11 for the experimental and control groups respectively. Results showed a highly significant reduction in MCV for the first record in the experimental group, and in the second record for the experimental group, MCV was still significantly reduced. Results of this study support the hypothesis that inversion ankle trauma is frequently accompanied by peroneal nerve lesions. Also suggest that MCV measurements can be a valuable tool in evaluating more objectively the functional instability of the ankle joint.