This independent study aims to 1) examine the marketing mix factors that influence decision-making behavior in purchasing an eco-car (ECO-Car), and 2) compare personal factors that affect decision-making behavior in the purchase of ECO-Cars. This research follows a quantitative approach. The sample for the study consists of 222 individuals from a province in Thailand, with the sample size determined using Taro Yamane's formula and selected through accidental sampling. Data were collected via questionnaires and analyzed using statistical methods such as Frequency, Percentage, Means, Standard Deviation, Independent Sample t-test, and one-way ANOVA, with a significance level set at 0.05. To further assess group differences, Scheffe Analysis was used for pairwise comparisons. The results indicated that 1) overall, respondents held high opinions regarding the factors affecting decision-making behavior in purchasing an ECO-Car. 2) Significant differences were observed when comparing opinions on factors influencing decision-making behavior, with 12 differences based on gender, 29 differences based on age, 13 differences based on marital status, 15 differences based on educational level, 26 differences based on occupation, and 26 differences based on income. All these differences were significant at the 0.05 level.