According to the constructivism learning theory, blog may act as a useful tool for improving writing capability. For this purpose, the present article attempts to explore the potential of blog for improving English writing in the Chinese tertiary EFL classrooms. A quasi-experimental study was conducted in a Chinese university to compare the effects between traditional in-class process-oriented writing instruction and blog integrated writing instruction. Result of the experiment shows that blog integrated writing instruction resulted in better writing performance. Therefore, the claim that blog may promote more effective writing instruction is substantiated.