Aims: Given the high prevalence of Internet gaming disorder (IGD) among university students and the beneficial effects of positive psychological factors on mental illness, the present longitudinal research aimed to investigate whether purpose in life and social support yields long-term results in protecting university students from IGD. Methods: We recruited 469 Chinese university students to voluntarily fill out an anonymous questionnaire at baseline, and 283 of them were followed up and given similar measures after one year. Results: The prevalence of probable IGD at the baseline and follow-up surveys was 14.8% and 9.9% respectively. Purpose in life and social support were negatively correlated with IGD symptoms in both surveys (p < .05). The results of a cross-lagged analysis showed that purpose in life, but not social support, assessed at baseline predicted fewer IGD symptoms at follow-up (p < .001). In addition, social support and purpose in life predicted one another across time. Conclusions: The prevalence of probable IGD was high among Chinese university students. Purpose in life was shown to be an effective significant protective factor against IGD, while the effect of social support might be indirect. Positive psychology interventions, which promote the search for and attainment life purpose, may be incorporated in school-based program for IGD prevention.