AimWorkplace social capital refers to relationship networks formed by individuals in an organization through long‐term mutually beneficial interactions and cooperation with members. These relationship networks can create value and resources for organizations and individuals. This current study aimed to explore the potential impact of workplace social capital on the association between perceived stress and professional identity in clinical nurses during the COVID‐19 outbreak.MethodsIn this cross‐sectional study, 308 Chinese clinical nurses filled out the Chinese Workplace Social Capital Scale, the Chinese Perceived Stress Scale, and the Chinese Nurse's Professional Identity Scale. Descriptive analysis, independent samples t test, analysis of variance, Pearson correlation analyses, and bootstrap method were performed to analyze the data.ResultsPerceived stress was negatively correlated with professional identity (r = −0.455, p < .001). Workplace social capital was not found to moderate the relationship between perceived stress and professional identity (95% CI −0.03 to− 0.06, p = .47 > .05). Instead, it mediated that relationship (95% CI −0.61 to −0.19, p < .05), and its mediating effect was −0.37.ConclusionsIn the early stages of the COVID‐19 outbreak, workplace social capital among the investigated clinical nurses failed to buffer the negative impact of perceived stress on professional identity, but it did play a part in mediating perceived stress and professional identity. A healthy workplace should be provided to clinical nurses to improve their professional identity, while lowering perceived stress.