Work placement has been regarded as one of the most effective ways of developing vocational teachers' occupational expertise. Guided by expectancy-value theory, we aim to explore how vocational teachers' motivation towards professional learning shapes to their engagement when on work placement. Two research questions were addressed: 1) What is the relationship between vocational teachers' motivational beliefs and engagement in work placement? 2) Does teaching experience have a moderating effect on this relationship? The data was collected from an online survey and analysed with a quantitative way. The participants were 426 Chinese secondary vocational teachers. Exploratory factor analysis identified four motivational beliefs: task value, self-efficacy, task effort, and emotional cost. Regression analysis revealed that vocational teachers' task value, self-efficacy, and task effort were positively related to their engagement. Teachers' emotional cost was negatively linked to their behavioural, cognitive, and emotional engagement, but positively linked to agentic engagement. Moreover, a negative moderation of teaching experience was seen. These findings facilitate the understanding of vocational teachers' professional learning in work site and provide suggestions on how to reinforce their engagement. The future research could examine the relationship between vocational teachers' motivational beliefs and engagement from a longitudinal perspective or within other learning contexts.