Unplanned purchase is an unexpected buying behavior affected by product or marketing stimuli. Unplanned purchase does not follow the order of the rational decision making process. Through an in-depth interview, this study classified the types of unplanned purchase of clothing and examined the decision-making processes. The results (according to the need recognition level of consumers prior to stimuli) show three types of unplanned purchase of clothing products that are classified as: the need-manifesting type, the need-embodying type, and the need-reminding type. In addition, each type is reclassified into the high-cognition type and the low-cognition type according to the cognitive effort level of consumers during the purchase decision-making process. The need-manifesting type recognized a buying need after exposure to stimuli and then engaged in unplanned purchases. The need-embodying type recognized a problem, but the purchase intention was not concrete. The need-reminding type recognized a desire to buy clothing products, but temporarily forgot it, and then later remembered the problem recognition from the past after experiencing the stimuli.