According as there are mediators or not, the microbial fuel cells could be classified in two classes: indirect microbial fuel cells and direct microbial fuel cells. The research progresses of direct microbial fuel cells in recent years were summarized. The operation principles of direct microbial fuel cells were described. Present researches of direct microbial fuel cells and the problems to be resolved were pointed out. Finally, the application prospect of direct microbial fuel cells was forecasted.