Purpose: To investigate the efficiency of a single-session character-strength-based cognitive intervention on enhancing freshmen's adaptability. Method: A randomized trial, pretest, posttest, follow-up intervention was employed using repeated-measures analyses to evaluate the effect. This 90-min intervention contained four activities with 52 undergraduate freshmen (age 17-20) randomly assigned to the intervention and control group, 38 of whom completed all the programs (19 of each group). Results: Compared with the control group, the intervention group showed a remarkable increase in well-being and a significant reduction in depression and anxiety at post and follow-up assessment. The stress level of the intervention group significantly decreased only at the follow-up test. Time effect and the interaction between time and group were significant in anxiety and stress. Conclusions: This intervention can quickly reduce negative affect and elevate well-being for freshmen. It expands the role of social worker in the prevention of mental illness among college population.