Objective To assess the value of bulbocavernosus reflex (BCR) in the differential diagnosis of Parkinson' s disease (PD) and multiple system atrophy (MSA).Methods BCR was compared in 55 patients with PD,20 patients with MSA,and 50 healthy controls,who were enrolled from the Department of Neurology,the First Affiliated Hospital of Wenzhou Medical University from May 2013 to April 2014.The clinical features of autonomic nerves dysfunction were also recorded.Results Among all related autonomic symptoms,the occurrence rate of constipation,urinary urgency and frequency in patients with MSA was higher than those with PD.The elicit percent of BCR in patients with PD was 93％,higher than those with MSA (70％).The average latency of BCR in patients with MSA was longer than those with PD (tmale left =16.275,tmale right =14.269,tfemale left =5.954,tfemmale right =5.905,all P ＜ 0.05).The degree of BCR amplitude decreasing in three groups was MSA ＞ PD ＞ healthy controls.There was statistically significant difference among three groups (Fmale left =75.73,Fmale right =73.13,Ffemale left =72.70,Ffemale right =59.44,all P ＜ 0.05).The area under receiver operating characteristic curve (ROC) in differential diagnosis of PD and MSA of the average latency of BCR in male and female was 0.947 and 0.948.The area under ROC curve in differential diagnosis of PD and MSA of the average amplitude of BCR in male and female was 0.886 and 0.920.The ROC curve showed the average latency of BCR in male of 44.80 ms with a sensitivity of 95％ and a specificity of 84％,and in female of 61.35 ms with a sensitivity of 86％ and a specificity of 88％ ; the average amplitude of BCR in male of 0.37 mV with a sensitivity of 96％ and a specificity of 68％,and in female of 0.36 mV with a sensitivity of 98％ and a specificity of 76％,which were critical cutoff values in differential diagnosis of PD and MSA with the best sensitivity and specificity.Conclusion The latency and amplitude of BCR test helps to increase the accuracy in the differential diagnosis of PD and MSA.