Even though computer games hold considerable potential for engaging and facilitating learning among today's children, the adoption of modern educational computer games is still meeting significant resistance in K-12 education. The purpose of this paper is to inform educators and instructional designers on factors affecting teachers' adoption of modern educational computer games. A case study was conducted to identify the factors affecting the adoption of "Dimenxian", which was a new educational computer game designed to teach Algebra to middle school students. The diffusion of innovations theory was used as the conceptual framework of this study. The results indicated that compatibility, relative advantage, complexity and trialability played important roles in the game adoption. These findings were compared with the existing literature on (1) the adoption of educational software, and (2) the barriers in the use of educational computer games in K-12 settings to help guide future research and practice. The comparison showed that (1) adoption attributes for the games and other educational software had a similar pattern from high to low significance: relative advantage, compatibility, complexity, trialability and observability; and (2) the game adoption factors were more inclusive than the barriers of using the computer games.