Blog's becoming the fastest communications tools and cheapest public relations handles for business. This paper aims to discuss the strategic implications of blogs marketing and proposes the conceptual framework, especially focusing the firm size variable as a key moderator. The roles of blog for marketing functions are different between big and small businesses. Blog has great impacts on SMEs such as boosting company's brand, speeding up the efficiency of product diffusion, improving the communications and maintaining brand-consumer relationship. The valuable findings are investigated by qualitative approach, and the discussion is supposed to be useful for SMEs' marketing practices in Taiwan.