Cell morphology measurement is important in evaluating the injury level of nervous system. However, current measurement process is mostly achieved by manual estimation which is subjective and time-consuming. We hence propose a two-stage method to automatically segment axons and myelin sheaths from microscopic images for measuring the cell morphology quantitatively. First, an automatic thresholding method is used to obtain axon candidates and then geometric and image properties are used to assure the axon regions. Second, the outer contour of myelin sheath is segmented using the active contour model with the obtained axon contour as the initial solution. Then, the desired morphological parameters can be readily measured. In the experiments, we used seven nerve images for accuracy validation and achieved very small contour distance errors (less than 0.5 μm with nerve diameter around 8 μm in average). Overall, the proposed method is found efficient and useful in nerve parameter evaluation.