This paper presents a measurement method of refrigerant mass faction in an ammonia-absorption refrigerator. The proposed method is modified from conventional sampling method In the conventional method, a certain volume of solution from the outlet of condenser is sampled under the atmospheric pressure. With the nature of the high volatility of ammonia, it is difficult to measure the solution volume with high precision. Therefore, authors modified experimental set-up with pressurized chamber in which the solution volume is measured with high precision. The experimental results showed good match with results of a prediction method developed by authors.