Abstract: A microcalorimeter used for radioactivity measuring of nuclides with pure β-emission was developed, and the dual-compensated isothermal microcalorimeter was designed. The best number of thermocouples was calculated. The data acquisition and processing software were programmed. The thermal power calibration for the equipment was carried out for designed and developed microcalorimeter. The uncertainty of calibration at 15 μW of input thermal power is within 2% for this microcalorimeter.