Social work in China faces the challenge posed by social workers’ increased professionalization but declining professional attachment. Besides external environmental factors, personality also affects professional competence and attachment. Building on Developmental Contextualism and the Big Five personality theory, this study examines how personality (i.e. extraversion and conscientiousness) shapes accredited MSW newcomers’ professional competence and attachment. Using latent growth modeling and data collected at three points in time from newcomers (N = 154), it was found that newcomers’ baseline trajectory of change in professional competence is positive, while that in professional attachment is negative. The initial level of professional competence mediates a negative relationship between extraversion and the declining rate of professional attachment. The findings provide empirical research evidence and insights for the effective identification and preparation of suitable social workers.