The study investigated the mediating role of anxiety in the predictiveness of students' attitude and motivation on their achievements in English for Specific Purposes (ESP) classes. A total of number of 424 students at the Faculty of Tourism in a state university in Turkey participated in the study in the Spring Semester of 2017-2018 academic year. The participants were selected randomly on voluntary basis. The data were collected using attitude, motivation and anxiety scales. The participants declared their success scores in the Vocational English Course (an ESP class). The data were analysed using the IBM SPSS 20 with Hayes (2013)'s PROCESS macro. Bootstrapped confidence intervals were used to examine the indirect effect of anxiety on the effect of attitude and motivation on achievement. The results revealed that there was a significant positive relationship between attitude and motivation, between attitude and achievement, and between motivation and achievement. A significant negative relationship was found between anxiety and attitude, motivation and achievement. The results also revealed that attitude predicted achievement positively and anxiety negatively; and that anxiety predicted achievement negatively. Anxiety partially mediated the predictiveness of attitude on achievement. The study found out that motivation predicted achievement positively and anxiety negatively. Anxiety partially mediated the predictiveness of motivation on achievement. Overall, in order to increase achievement, attitude and motivation levels of students should be increased and anxiety levels should be reduced as much as possible.