Background: Second language (L2) learning is complex, multifaceted, and greatly influenced by various factors, of which individual factors like anxiety and motivation are important ones. Though anxiety and motivation have been shown to be strongly correlated with each other and interact with other variables to collaboratively affect L2 learning, mixed findings have been revealed, demonstrating the complexity of the interrelationship between L2 anxiety and motivation and their interactive effects on L2 learning. Purpose: Guided by the self-determination theory, this study aimed to explore the levels of and the relationship between English classroom anxiety and motivation as well as their predictive effects on Chinese undergraduate EFL (English as a foreign language) learners’ English achievement. Method: The participants were 571 Chinese university students who answered an 8-item English Classroom Anxiety Scale, a 35-item English Learning Motivation Scale, and a 5-item Demographic Information Questionnaire. They also reported their scores in tests that they had recently taken and self-rated their overall English proficiency as indicators of their English achievement. Results: The study revealed the following major findings: (a) the participants had a small to moderate level of English classroom anxiety, and a medium level of intrinsic motivation, extrinsic motivation, personal goals and expectancy/control in English learning, (b) English classroom anxiety was significantly negatively correlated with all motivation scales, (c) English classroom anxiety was not only significantly negatively related to but negatively predicted the students’ English achievement, and (d) significantly positive correlations existed between English learning motivation and English achievement. Of different motivation dimensions, intrinsic and extrinsic motivation positively predicted the latter. Conclusion: The findings of this study further demonstrate the importance of anxiety and motivation in L2 learning and the need to explore anxiety-reduction strategies, increase students’ intrinsic and extrinsic motivation, and strengthen their expectancy in L2 teaching and learning, thus contributing to the understanding of foreign language anxiety and L2 motivation and enriching the current literature on the two issues.