Gym clubs not only play the role of a fitness place for physical exercise, but also serve as a social place that provides enjoyment. This study aims to investigate the relationship between gyms’ indoor environmental quality (IEQ) and customer emotion with the mediating roles of perceived service quality and perceived psychological safety. Using a large sample data of 888 gym customers in Vietnam, results of structural equation modelling reveal a positive relationship between gyms’ IEQ and customer emotion. Furthermore, perceived service quality and perceived psychological safety positively mediate this relationship. Perceived psychological safety also appears to have a mediating effect on the perceived service quality-customer emotion association. These findings provide insights for gyms’ administrators and managers to better understand different elements of IEQ and the role of service quality. Based on this understanding, they can improve their gyms’ IEQ to generate positive customer perception and emotion.