The inverter rotary compressor discharges refrigerant and compressor oil in air-conditioning systems. The compressor oil which discharged form compressor decreases the efficiency of heat exchanger and affects the compressor operation. Recently, several studies are in progress for reducing the compressor oil. Before the reduction of compressor oil discharge rate, the quantitative measurement and evaluation method are required. In order to cope with this requirement we have developed the measurement technic of oil discharge rate. The reliability assessment was carried out approximately 0.1% of the errors with compressor performance indicators. The acceptable errors were to ensure the reliability of measurement technic. In the experiment results at several conditions, The oil discharge rate of heating operation has been confirmed average 3.7 times more than cooling operation. In this study the evaluation method and the experimental results of oil discharge rate in air-conditioning systems are presented with various operating conditions.