Background: Physical activity (PA) has shown numerous benefits in preschoolers (2.9–5 years). Preschoolers aren’t meeting recommendations for adequate daily PA. Novel techniques are needed to increase PA via intervention within the preschool center, where preschoolers spend much of their weekdays. Karate has shown promise for improving health (e.g., fitness, behavior) in elementary school-age children. No studies have examined the effects of karate on PA or behavior in preschoolers. The purpose of this study was to examine the feasibility and preliminary efficacy of a 6-week karate-themed PA intervention on PA and classroom behavior in preschoolers. Methods: The intervention was implemented 20 minutes per session, three days per week, for six weeks. Process evaluation data was collected during each session using a semi-structured questionnaire. One randomly selected day per week, participants wore accelerometers during the intervention to measure intervention intensity. At baseline and six weeks, participants' school day PA and teacher-reported classroom behavior were assessed using accelerometers and the Strengths and Difficulties Questionnaire, respectively. Results: The participants (n=29) were 72.4% male, 44.4% African American, and 44.4% Hispanic. The average age of participants was 4.35±0.47 years, and the average BMI percentile was 72±32.3. The program exhibited low fidelity, with 28% of intervention sessions implemented as intended, and low intensity, with participants spending 57%±17.9% of intervention time sedentary, 15.1%±6% in light PA, and 27.9%±14.3% in MVPA. The program exhibited high quality, with 100% of intervention sessions implemented clearly and 95.6% of sessions implemented correctly, and high acceptability, with preschoolers enjoying the sessions 97.8% of the time and preschoolers paying attention 100% of the time. Percent time spent sedentary during the preschool day significantly increased from baseline (78.3%±4%) to six weeks (87.6%±5.9%). Percent time in light PA significantly decreased from baseline (9.4±1.8%) to six weeks (5.9%±2.6%), as did MVPA from baseline (12.3%±2.9%) to 6 weeks (6.6%±3.4%). Participants’ total difficulty scores for behavior significantly improved from baseline (10.6±8.7) to six weeks (9.0±7.7). Conclusion: Overall, the high quality, acceptability, and efficacy of teacher-reported classroom behavior highlight KIP’s potential in preschoolers. More studies are needed to examine the effects of karate-based physical activity interventions in preschoolers.