Currently, a paramount issue in nursing education is to motivate nursing undergraduate interns to develop self-directed learning skills and improve their practice satisfaction and professional identity, so as to meet the growing demands in healthcare. This study aimed to examine the effectiveness of a motivational programme based on the Existence-Relatedness-Growth (ERG) theory in developing self-directed learning skills, improving practice satisfaction and promoting the professional identity of nursing undergraduate interns in China. A quasi-experimental study design. A government-funded tertiary teaching hospital in Guangzhou, Guangdong province, China. This study was conducted with 99 nursing undergraduate interns in a hospital between June 2020 and April 2022. The interns in the experimental group (n = 50) participated in the motivational programme based on ERG theory, while those in the control group (n = 49) underwent a traditional training programme. The interns in the two groups were compared in terms of their degree of self-directed learning, practice satisfaction and professional identity after the training, using independent samples t-test. After the internship, interns in the experimental group showed a statistically significantly higher level of self-directed learning and practice satisfaction than those in the control group (p < 0.05). However, no significant difference was observed in professional identity between the two groups after the internship. The motivational programme based on ERG theory was shown to be effective in improving self-directed learning and practice satisfaction in nursing undergraduate interns. A large-scale randomized controlled trial is warranted to confirm the results.