Aim of this research aim to develop an Android-based Rhythmicgym application to improve the rhythmic gymnastics skills of Yogyakarta City Middle School students. Method of this research use development (R&D). This research procedure adapts the ADDIE development model ( analysis, design, development, implementation, evaluation). The research subjects were divided into three groups, namely: (1) three expert lecturers (2) small-scale tests were tested on 36 students and one Physical Education teacher, (3) large-scale tests were tested on 72 students and one Education teacher Physical. Data collection instruments used questionnaires and observation rubrics. The data analysis technique in the validation test uses Aiken V analysis, the feasibility test questionnaire is analyzed using a Likert scale Results The results of the material and media instrument validation tests obtained an average Aiken V value of 0.883 and 0.937 respectively with a very high validity category . The results of the instrument reliability test for material and media instruments respectively with Cronbach's Alpha values of 0.761 and 0.652 mean that the instrument is declared reliable. The results of small-scale trials on 36 students and one Physical Education teacher showed a percentage of 78% in the appropriate category. The results of a large-scale trial that was tested on 72 students and one Physical Education Teacher showed a percentage of 81% with a very feasible category. Conclusion Based on the research results, it can be concluded that the Android-based RhytmicGym application is declared valid, reliable, feasible, practical and effective for improving the rhythmic gymnastics skills of Yogyakarta City Middle School students.