The objectives of this research were (1) to study personal influence on purchasing decision behaviour of Boom collagen dietary supplement products of consumers in Chiang Mai province, Thailand, and (2) to study the influence of marketing mix affecting purchasing behaviour of Boom collagen supplement products of consumers in Chiang Mai province, Thailand. This research is quantitative research. The sample group used in this research was 400 consumers in Chiang Mai province using convenient random sampling. Questionnaires were used as a tool to collect information. The statistics used in the analysis were mean, standard deviation, difference, the mean value, one way variance and Pearson's simple correlation coefficient statistic. The results of the study found that influence on marketing mix:  product, price, distribution channel and marketing promotion. The opinion level was at a high level in all aspects. The hypothesis testing found that (1) personal influences were different gender, age and occupation. The behaviour of decision to buy Boom collagen products is not different in term of the level of education, and 2) the influence of the overall marketing mix and of each aspect has the decision-making behaviour of the Boom collagen supplement products and the frequency of purchases had no relationship.