Objective: Interest in health videogames to stimulate health behavior change is increasing, yet little research exists on their use. This study tested the acceptability of an online health videogame called ''Fitter CrittersÔ'' (Megazoid Games, Collegeville, PA) for improving healthy diet and activity in elementary school students. Subjects and Methods: In October and November 2011, fifth grade students (n = 97) from a school in central Massachusetts played the game for 1 week during their health class. Measures of nutrition and activity knowledge, attitudes, and self-efficacy were completed prior to playing the game and again on the final day along with a videogame acceptability questionnaire. Results: The videogame was highly acceptable to participants as measured by the acceptability questionnaire mean rating of 4.52 (SD = 0.60), where 1 = strongly disagree and 5 = strongly agree; 73% of students played the game at least once outside of class. Significant increases in positive attitudes toward healthy eating (P < 0.001) and healthy eating self-efficacy (P = 0.02) and marginally significant increases in nutrition knowledge (P = 0.08) were observed. Conclusions: The ''Fitter Critters'' health videogame engages students in learning about healthy eating and activity. Further research should assess whether the positive changes observed in knowledge, attitudes, and selfefficacy translate into behavior change.