The aim of this study is to illustrate the causal relationship among brand extension, trust, and new product performance. We found that brand trust is positively influenced by brand extension in market activities. Trust is an important element and it’s hard to build up and maintain because customers would consider the firms image when purchasing high-priced merchandises. We found that brand trust has a positive causal relationship on market performance. We suggest the managers in the jewelry industry should make good marketing in their products then building excellent goodwill. After that the company would have outstanding performances.