Social capital has been receiving increasing attention in HRD research. However, the sources of social capital have received inadequate attention. Little has been done to reveal how people obtain their social capital in the workplace. This study investigated the effects of employees' altruistic citizenship behavior and job involvement on their advice network centrality. Advice network centrality was used as an indicator of social capital. The results suggest that altruistic citizenship behavior and job involvement are positively associated with employees' advice network centrality. Furthermore, our findings suggest that job involvement moderates the effect of altruistic citizenship behavior on advice network centrality. Theoretical and practical implications for HRD are discussed and future directions are drawn. (Contains 2 tables and 2 figures.)