To clarify the function of the puborectalis muscle(PM)in fecal incontinence(FI)prevention after low anterior resection (LAR)for lower rectal cancer(LRC), PM function at 3 years after LAR was studied. A total of 29 patients aged 40-79 years (19 men and 10 women, mean age: 63.9 years)who underwent LAR for LRC were enrolled in the present study. Based on the presence of postoperative FI, these patients were divided into 2 groups[group A: patients with FI(n=13), 11 men and 2 women aged 43-75 years(mean age: 64.8 years)and group B: patients without FI(continence, n=16), 8 men and 8 women aged 41-79 years(mean age: 62.9 years)]. These groups were compared with group C of control subjects[n=38; 28 men and 10 women aged 42-76 years(mean age: 64.5 years)]. Magnetic stimulation at the S2-4 sacral levels has been shown to activate the sacral motor nerve(SMN)root of the cauda equina. SMN latency(SMNL)was determined on the right, left, and posterior sides of the upper anal canal. FI after LAR was also evaluated using the Wexner score(WS), with a score of 8 or more being associated with FI according to our data. All patients had pathological Stage Ⅰ disease(19 patients: T1, N0, M0; 10 patients: T2, N0, M0). Group A had a larger proportion of men than group B(p<0.1). The distance of anastomosis from the anal verge(DAAV)was significantly shorter in group A(2.2±1.2 cm)than in group B(4.6 ±1.3 cm)(p<0.001). Regarding WS of group A, 23.1% patients had a score of 8-10(mean: 9.0), 53.8% of 11-15 (mean: 13.4), and 30.7% of 16-20(mean: 17.0). All patients in group A(WS: 8 or more)were incontinent. In contrast, all patients in groups B(WS: 0)and C(WS: 0)were continent. Patients with preoperative defecation ability(WS: 0)were also continent. As for SMNL on the right(9 o'clock), left(15 o'clock), and posterior(18 o'clock)sides of the PM located in the upper anal canal, conduction delay was significantly longer in group A(8.4±0.6 ms, 8.2±1.9 ms, and 8.3±0.9 ms, respectively)than in groups B(4.4±0.5 ms, 4.3±0.7 ms, and 4.4±0.9 ms, respectively)and C(4.1±0.5 ms, 4.0±0.5 ms, and 4.2±0.7 ms, respectively)(p<0.001, all). FI after LAR with a short DAAV, especially in men, may cause PM dysfunction due to operative damage of the SMN.