Background: Effective training transfer experiences at healthcare organizations contribute to decent professional health care trainers who equip their trainees to exhibit professionalism in their daily clinical practice. Aim: Determine the effect of training transfer program on development of nursing trainees' professional competencies. Setting: The present study was implemented at Tanta International Teaching Hospital. Participants: A purposive sample (n= 330) was used. This sample was divided into two groups, group I; all qualified nursing trainers (n=30) and group II; nursing trainees (n=300) Tools: Three tools were used namely; Training Transfer Knowledge Questionnaire (TTKQ), Training Transfer Domains Questionnaire, and Professional Competencies Development Self-report Results: Preprogram 80.0% of trainers' knowledge level was at a poor level improved to (86.7%% and 70%) of their knowledge be at the good level immediately post-program and 3 months post-program respectively. A high percent (72%) of trainees pre-program had unsatisfactory practice level of professional competencies improved to 83 % of them have satisfactory practice level of professional competencies three months post-program. Conclusion: There were improvements in nursing trainers' knowledge and practice regarding effective training transfer domains after the implementation of the designed program than pre-program. Nursing trainees' professional competencies were developed after the implementation of the designed program compared to the pre-program. Recommendations: Conducting periodic educational training program and workshop about effective training transfer.