Serious games have been commonly used in information technology education and training. Many of them are multi-player games. Competition can be intuitively associated with games. However, research results of the learning impact of competition are mixed. Challenge and control are two game attributes which are highly relevant to competition. With the use of a multi-player serious game, SEO War Online, this study aims to explore the relationships among perceived competition, perceived control, perceived challenge, and self-efficacy in a serious gaming environment. Particularly, it examines whether competition helps learning in a serious gaming environment and whether challenge and control are two major mechanisms through which competition generates learning effects. The study advances our understanding of whether and how competition derives self-efficacy. It contributes to expanding literature on selection of important game attributes. It helps game designers determine whether competition is an important game attributes through which game optimization can be achieved.