This study aims at investigating to what extent willingness to communicate in English mediate the relationship between foreign language speaking anxiety and speaking achievement of the EFL students in tertiary education. Using a multiple regression, the researchers analyzed foreign language speaking anxiety (FLSA) as the predictor variable, willingness to communicate (WTC) as the mediator variable and speaking achievement as the dependent variable. The respondents were 50 EFL students of the faculty of teacher training and education, Mulawarman University in Indonesia. The researchers used three instruments, namely: 1) modified version of Foreign Language Classroom Anxiety (FLCAS) questionnaire, 2) willingness to communicate in English questionnaire, and 3) speaking test. The data were analyzed by using simple linier and multiple regression. The result of this study revealed that a) FLSA significantly predicted speaking achievement B = -.36, t(48) = -6.10, p < .001 (the negative coefficient (B = -.36) showed that if the speaking anxiety increased, speaking achievement tended to decrease); b) FLSA significantly predicted WTC, B = -.32, t(48) = -5.63, p < .001 (students who have increasing level of speaking anxiety tend to decrease their WTC level (B = -.32); and; c) WTC significantly predicted speaking achievement of the students, B = .87, t(48) = 10.27, p < .001 (the positive coefficient (B = .87) suggested that students who were willing to communicate in the classroom tended to score higher in speaking achievement). The final result of regression indicated that FLSA and WTC explained 72% of the variance, R² = .72, F (2, 47) = 60.03, p < .001. This implies that students’ speaking anxiety might be kept constantly low in order that the EFL students have willingness to speak in English.