Purpose: To demonstrate the value of sequential determinations of pelvic drainage in the identification ofincreased risk of anastomotic leakage (AL) after anterior resection for rectal cancer with a double staplingtechnique. Patients and Methods: Between January 2004 and December 2011, data for the daily postoperativepH of pelvic drainage fluid in 753 consecutive patients with rectal cancer who initially underwent anteriorresection with a double stapling technique were reviewed. All patients experienced a total mesorectal excision.Patients with anastomotic leakage (Group AL, n=57) were compared to patients without leakage (Group nAL,n=696). Patients with perioperatively abdominopelvic implants that were likely to affect pH value (determinedat 25 ℃) other than leakage were excluded. Mean postoperative values were compared. Results: Anastomoticleakage was noted in 57 (7.6%) of 753 patients with rectal cancer. The diagnosis of anastomotic leakage wasmade between the 6th and 12th postoperative day (POD; mean 8th POD). There was no significance of the dailyaverage values of pH on POD1 & 2 in group AL while a significantly sharp declining mean pH value reachedits diagnostic point of AL (p<0.001) on POD3. A cut-off value of 6.978 on the 3rd POD maximized the sensitivity(98.7.0%) and specificity (94.7%) in assessing the risk of leakage. Conclusion: According to these results, anearly and persistent declining of pH value of pelvic drainage fluid after rectal surgery with anastomosis, is amarker of AL. A cut-off value of 6.798 on POD3 maximizes sensitivity and specificity.