The purposes of this research were studied personal factors affecting the decision on purchasing products from Japanese Department store of Siam Takashimaya, including customer behavior of the population in Bangkok affecting the decision on purchasing products from Japanese Department store of Siam Takashimaya and the relationship between the 7Ps Marketing Mix factors and the decision on purchasing products from Japanese Department store of Siam Takashimaya in Bangkok. This study was a quantitative research, the sample group was 400 people living in Bangkok who have purchased products of Siam Takashimaya. A questionnaire was used as a tool for data collection. The statistics used for data analysis were percentage, mean, standard deviation, statistical analysis of T-test, F-Test and multiple linear regression analysis.

            The results of this research were as following; 1) Personal factors in term of age, marital status, career, and average monthly income were the main factors which affected significantly on their decision. 2) Factors of customer behavior, in term of purchase intention Japan brands only, average bill per time, influencers of decision, and timing, were the main factors on their decision and 3) Factors of Marketing Mix (7Ps), in term of price, place, promotion, people, process, and physical evidence, were the main factors on their decision.