Title:  The effects of online third-party opinions toward Consumer Purchasing Decision on cosmetics products in Thai market Seminar date: June 4th , 2012 Course: Master thesis in International marketing, 15 credits Purpose: The overall purpose of this research is to explain the understanding of the effects of online third-party opinions toward consumer purchasing decision process on cosmetics products in Thai market. This includes the investigation of effective used of online third-party opinions with regards to source credibility and product involvement, specifically toward cosmetics products. Theoretical framework: The theoretical framework of this research is based on literature concerning online third party opinion, consumer decision journey (CDJ), product involvement and source credibility. Methodology: Both quantitative and qualitative method was applied. And thus a questionnaire with 147 respondents on Thai market and two interviews of expert marketers were conducted. The respondents for questionnaire are Thai women with specific age range and criteria. Conclusion: The online third-party opinion plays the important role in nowadays in the marketing perspective. And it does affect the consumer purchasing decision process both pre-purchase and post-purchase stage. However, it mostly affects in Consider and Evaluation Stage. With regards to the product involvement and source credibility applying to cosmetics products, these two variables affect to the use of online third-party opinion. Online third-party opinion works best with high involvement product. However, low involvement product also be considered as suitable to use with online third-party opinion. For source credibility, both online expert and consumer reviews perform better when using with high involvement product comparing with low involvement one.