Objective To gain insight into the changes in psychological factors during rehabilitation after Achilles tendon rupture (ATR) and to explore the association between psychological factors during rehabilitation and functional outcome 12 months after ATR. Methods Fifty patients clinically diagnosed with ATR were invited to visit the hospital 3, 6, and 12 months after injury for data collection. They completed questionnaires assessing psychological factors: psychological readiness to return to sport (Injury Psychological Readiness to Return to Sport Questionnaire), kinesiophobia (Tampa Scale for Kinesiophobia), expectations, motivation, and outcome measures related to symptoms and physical activity (Achilles Tendon Total Rupture Score), and sports participation and performance (Oslo Sports Trauma Research Centre Overuse Injury Questionnaire). To determine whether psychological factors changed over time, generalized estimating equation analyses were performed. Multivariate regression analyses were used to study the association between psychological factors at 3, 6, and 12 months and outcome measures at 12 months after ATR. Results Psychological readiness to return to sport improved, and kinesiophobia decreased significantly during rehabilitation. Psychological readiness at 6 and 12 months showed significant associations with sports participation and performance. Kinesiophobia at 6 months was significantly associated with symptoms and physical activity. Motivation remained high during rehabilitation and was highly associated with symptoms and physical activity, sports participation and performance. Conclusion Psychological factors change during rehabilitation after ATR. Patients with lower motivation levels during rehabilitation, low psychological readiness to return to sports, and/or high levels of kinesiophobia at 6 months after ATR need to be identified. Impact According to these results, psychological factors can affect the rehabilitation of patients with ATR. Physical therapists can play an important role in recognizing patients with low motivation levels and low psychological readiness for return to sport and patients with high levels of kinesiophobia at 6 months post-ATR. Physical therapist interventions to enhance motivation and psychological readiness to return to sport and to reduce kinesiophobia need to be developed and studied in the post-ATR population. Lay Summary If you have Achilles tendon rupture, your level of motivation, psychological readiness for return to sport, and fear of movement can affect your rehabilitation outcome. Your physical therapist can help you recognize these factors.