Purpose This study aimed to confirm the mediating effects of transition shock on the relationships among grit, social support, and retention intention of new graduate nurses. Methods A total of 174 new graduate nurses were recruited from a university hospital and a general hospital. The data were collected between November and December 2022 and analyzed using descriptive statistics, independent t-test, one-way analysis of variance, Scheffé test, Pearson’s correlation coefficient, Baron and Kenny’s three-step regression analysis, and the PROCESS Macro Model 4. Results Nurses’ retention intention was positively correlated with grit (r=.56, p<.001) and social support (r=.48, p<.001) and negatively correlated with transition shock (r=-.56, p<.001). The mediating analysis revealed that transition shock mediated the relationship between grit and retention intention as well as between social support and retention intention. Conclusion Based on the findings, an intervention program should be developed to reduce transition shock in new graduate nurses to increase their intention of retention.