This study aimed to examine the relationship between internet use (constructive and health-related internet behavior, health app usages), physical activity self-efficacy, and subjective well-being (quality of life, health satisfaction, sleep satisfaction). Participants (N = 758) were recruited to participate in an online survey. One-way MANOVA and multiple regression analyses were used to examine the hypotheses. Results showed that internet use was negatively associated with sleep satisfaction, r(738) = -.127, p < .001. Individuals who use health-related apps for movement/fitness, t(689.900) = -3.354, p < .001, nutrition, t(300.075) = -2.434, p = .016, information for self-diagnosis, t(199.768) = -2.321, p = .021, and contact with doctors, t(90.630) = -2.035, p = .045, have higher PA self-efficacy than those who do not. Overall, there was a statistically significant difference in subjective well-being based on a participants’ constructive internet use, F(28, 2590) = 1.97, p = .002, with quality of life (p = .006) and sleep satisfaction (p = .025) being statistically significant components of subjective well-being. This paper discusses the important theoretical and practical implications regarding the development of health-related apps and online well-being interventions which are significantly relevant to the well-being literature.