This longitudinal study examined the developmental trajectories of prosocial behavior and related predictors among adolescents exposed to the 2008 Wenchuan earthquake. At 6-, 18-, and 30-months postearthquake, we followed a sample of 1,573 adolescents. Self-report measures were used to assess earthquake exposure, postearthquake negative life events, prosocial behavior, symptoms of posttraumatic stress disorder, depression, anxiety, social support, and coping style. Data were analyzed using growth mixture modeling and multinomial logistic regressions. Four trajectories of postearthquake prosocial behavior were identified in the sample: (a) high/enhancing (35.0%), (b) high/stable (29.4%), (c) low/declining (33.6%), and (d) low/steeply declining (2.0%). Female gender, more social support, and greater positive coping were significant factors related to a higher probability of developing the high/enhancing trajectory. These findings may be helpful for us to identify adolescents with poor prosocial behavior after exposure to earthquakes so as to provide them with appropriate intervention.