Brand management is the significant issue in the competitive business environment, for example, specialize a brand among many choices for consumers. The present paper explores the synergy and effects of brand alliance from BenQ-Siemens case by survey. The results reveal the consumers' perception and cognition for BenQ-Siemens and the effects of brand personality for brand alliance. The relationships between the customers and companies become dynamic and unpredictable in the existing business environment. Companies attempt to build a strong brand image in order to attract customer attention and bind the relationships. That is, brand is not only a company name but an embedded image for customers. The enterprises can attain high market share if they identify the personalities and specialization of their brands. Brand alliance is a special strategy for brand management which combines two brands to a single brand with a unified name. Brand alliance is a branding strategy used in a business alliance. Brand alliance, which has become increasingly prevalent, is defined as a partnership or long-term relationship that permits partners to meet their goals (Cravens, 1994). For instance, Sony-Ericsson is a successful paradigm for brand alliance through joint venture. The synergy of brand alliance is unpredictable and potentially powerful. BenQ, the top 10 brand in Taiwan, merges the Siemens' telecommunication department in 2005. Despite the outcome is failure for two companies, the brand image and personality are worthy to explore from customer perspective.