A new method was presented to study the content of the soluble alkali in mortar. The method was based on mixing powdered sample with distilled water with two water-solid ratios and measur-ing the pH of the suspension. According to the measurement result of the suspension, the content of soluble alkali in mortar was calculated. The parameters such as water-solid ratio and measuring ac-curacy which affected the calculated result were investigated. The calculated result of the content of soluble alkali in mortar was compared with the result of flame photometry. The calculation was in good agreement with the result of flame photometry.