The hydrolysis of iminodiacetonitrile (IDAN) in near-critical water, without added catalysts, has been successfully conducted with temperature and residence time ranges of 200-260 degrees C and 10-60 min, respectively. The effects of temperature, pressure, and initial reactant/water ratio on the reaction rate and yield have been investigated. The final reaction products primarily included iminodiacetic acid (IDA) and ammonia associated with other by-products; gas formation was negligible. The maximum yield of IDA was 92.3 mol.-% at 210 degrees C and 10 MPa, with a conversion of almost 100 %.The apparent activation energy and In A of IDAN hydrolysis were evaluated as 45.77 +/- 5.26 kJ/mol and 8.6 +/- 0.1 min(-1), respectively, based on the assumption of first-order reaction. The reaction mechanism and scheme were similar to those of base-catalyzed reactions of nitriles examined in less severe conditions.