Aim: The present study aims to design, manufacture, and evaluate the performance of an active liquid cooling vest (ALCV) to control the heat strain in hot laboratory conditions. Materials and Methods: An ALCV was designed with a cold liquid circulation system in tubes embedded inside the vest. A performance of ALCV in the hot laboratory conditions with an average temperature of 38.5°C and relative humidity of 40% was done with ALCV and none-ALCV (NALCV). Parameters such as heart rate, oral temperature (OT), thermal sensation (TS), perceived exertion (PE), and chest temperature (CT), forehead temperature (FT), and scapula temperature (ST) were measured. Paired t-test was used to compare the average of the data. Results: The results illustrated that the difference between the average temperature of the ST and CT with ALCV and NALCV, it was 2°C ± 0.5°C. There was a statistically significant difference between the average PE and TS in two testing conditions (P < 0.05). Paired t-test showed that there is no significant difference between the average FT and OT in the two testing conditions (P > 0.05). Conclusion: Due to the positive effects of the designed ALCV in reducing skin temperature, heat sensation, and PE, this cooling vest can be used as a useful and cost-effective solution to reduce the level of heat strain in hot environments.