Although studies of nonrational consumer behaviour in the fields of psychology and marketing are widespread, few scholars have discussed this issue from the integrated perspective of individual characteristics and consumer welfare. Extant research has introduced the concept of consumer vulnerability to deepen the study of nonrational behaviour. The present research defines consumer vulnerability as an individual characteristic, that is, a tendency to be influenced by an external stimulation or temptation that leads to decisions harmful to the person's own welfare. To operationalize this concept, this study develops a consumer vulnerability scale. Results from exploratory factor analysis and confirmatory factor analysis reveal the following seven dimensions of consumer vulnerability: product knowledge, product promotion, marketing and emotional stress, social pressure, purchasing power, refunds policy and discrimination ability. After verifying the scale's reliability and validity, this study confirms that it can be applied to measure the degree to which consumer welfare has been harmed and predict nonrational decision‐making behaviour. Limitations and future research directions also are discussed.