<p>This assessment aims to develop an instrument for assessing the basic techniques of forehand and backhand groundstrokes for junior tennis players in Gunungkidul Regency because the basic forehand and backhand groundstrokes are very important in the game of tennis. This research design was a research that used the Research and Development (R&amp;D) stage which adopted the 4-D model of the instrument used in the form of assessment sheets for material experts, trainers, and athletes. Qualitative data analysis in the form of criticism, suggestions, and opinions of material experts, coaches, and athletes.<br />This assessment aimed to develop instruments for assessing basic forehand and backhand groundstroke techniques for junior tennis players in Gunungkidul Regency. This study used research and development methods with the 4-D method consisting of define, design, development, and dissemination with the following steps: (1) collecting information in the field, (2) analyzing the information obtained, (3) developing the initial product (4) expert validation and revision, (5) small-scale trials and revisions, (6) large-scale trials and revisions, (6) finalization and manufacture of assessment instrument products. The subjects in this study were junior tennis players in Gunungkidul Regency. Data analysis for validity testing was carried out using CVR (content validity ratio) and reliability using Alpha Cronbach. This research results in a basic technique assessment instrument product for forehand and backhand groundstrokes for junior tennis players which contains instructions, task sheets, scoring guidelines, scoring rubrics, and scoring tables that have high validity and hhigh-reliabilityforehand groundstroke initial attitude: r = 0.861, implementation r = 0.920, and final attitude 0.853. Backhand groundstroke initial attitude: r = 0.817, implementation attitude r = 0.871, and final attitude r = 0.824.</p><p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/soc/0019/a.php" alt="Hit counter" /></p>