n this thesis, the researcher investigates Factors influential in the decision to purchase third-generation (3G) mobile phones in Bangkok, Thailand. Using the multi-stage sampling technique and thence, the simple random sampling method, the researcher selected a sample population consisting of 400 residents of Bangkok, Thailand;who were fifteen years age or older and who had purchased or used mobile phones. The sample size was determined by means of an extrapolation from the Taro Yamane table at the statistically significant of 0.5 with the margin of error being set at ±5 percent. Using techniques of descriptive statistics, the researcher analyzed the data collected in terms of frequency, percentage, arithmetic mean and standard deviation. The Pearson correlation method and stepwise multiple regression analysis was also employed by the researcher.　　The findings are followed:(1) Most of the subjects under study were married males between the ages of twenty-six and thirty-five. Their educational level was at the bachelor’s degree and they had an average monthly between 10,000THB and 25,000THB and they were private company employees. (2) When considering the opinions of these consumers toward the factor marketing mix for 3G mobile phones, it was found that in an overall picture most of these subjects of investigation help opinions on an excellent level in respect to product, price, distribution Channel, and marketing promotion. When considered at the level of knowledge and understanding regarding 3G mobile phones, it was found that the subjects under study evinced knowledge and understanding of 3G mobile phones at a moderate level. Most of them had exhibited a tendency to buy 3G mobile phones. (3) In investigating the relationship between the decisions to purchase 3G mobile phones and factors of product, price, distribution Channel, marketing promotion, and the level of knowledge and understanding evinced concerning 3G mobile phones, the researcher found that the factors and the level of knowledge and understanding were directly at the statistically significant level of 0.5. In addition, the decision to buy 3G mobile phones was determined to be inversely correlated with the demographic characteristic of age with respect to the twenty-six to thirty-five age range in the statically significant level of 0.5. (4) Moreover, it was also found that the predictive equation governing the decision to purchase 3G mobile phones could be expressed.