Heat of hydrolysis of sucrose by yeast invertase at pH 4.6 and at 30°C was measured with a twin conductive micro-calorimeter, and was found to be Δ H = -14.75 kJ/mol. This value quite agreed with that of hydrolysis with acid reported by Sturtevant. It was found that mean deviation was 0.016 J and relative mean deviation was 0.54%, which suggested that the measurements were accurate. This method was applied to quantitative and selective analysis of sucrose in two foods, and the contents of sucrose in a canned coffee drink and Yokan were found to be 3.4 and 60.1 g/ 100 g, respectively.