Introduction Despite much cross‐sectional research linking prosocial behavior and meaning in life, few studies have investigated the longitudinal relationship between these two constructs. The article examines the bidirectional longitudinal association between prosocial behavior and meaning in life among junior high school students. Methods A prospective design was adopted, incorporating three measurement occasions (with approximately 6‐month intervals, from 2020 to 2021). Data were collected from 764 students (mean age = 12.46, SD = 0.64 years, and 51.4% girls). All participants responded to a questionnaire survey that included the Chinese Meaning in Life Questionnaire (MLQ‐C) and Prosocial Tendencies Measure (PTM‐C). Cross‐lagged panel models were used to analyze the data. Results (1) Prosocial behavior predicted positively the presence of meaning over time and vice‐versa. (2) There was no bidirectional association between the search for meaning and prosocial behavior. (3) There was no gender difference in the bidirectional relationship between meaning in life and prosocial behavior. Conclusions These findings suggest that educators should highlight the presence of meaning in adolescent life education from a long‐term perspective and encourage students to engage in more prosocial activities.