The Thai jewelry industry is considered a crucial industry, which contributes to the country growth. The industry is in the process of transformation, and is gradually shifting from Original Equipment Manufacturing (OEM), to Original Brand Manufacturing (OBM) businesses. However, Thai SME jewelers are facing the challenge of international competition, shortage of new generation human resources and changes in consumer behavior. To be able to survive, SMEs ought to build and enhance their competencies especially marketing competencies. This study thus adopted qualitative research based on 4 marketing leading SME case studies. The results showed that no matter whether the SME jeweler with stand-alone or chain store types, four marketing competencies, which are, product management, trust building, store and Location management, and Sales presentation are the key competencies that all cases regarded as vital contributions to their success in a competitive market.