Active communication is an important element of second language (L2) learning, as it contributes to the acquisition of language competence. The prerequisite of L2 use is having the willingness to communicate (WTC). However, previous research tended to conflate WTC and communication behaviour and provided little evidence that WTC and/or communication behaviour actually improve language attainment. This study aims to distinguish between WTC and actual communication behaviour and to analyse how they may influence language performance at both the trait and state levels. The participants included a sample of 31 undergraduate English majors at a Chinese university. Their WTC, communicative behaviour and language performance were measured at both the trait and state levels via self-reports and teacher reports. In addition, group interviews were conducted to gain further insight into the differences between WTC and communication behaviour. The study revealed inconsistencies between state WTC and actual communication behaviour. Compared with WTC, communication behaviour was a better predictor of language performance. This study highlights the importance of distinguishing WTC from actual communication behaviour and constitutes an appeal to language teachers to strive for translating learners' subjective communication intentions into actual communication behaviour to facilitate their language learning.