Although Vietnamese consumers have become more knowledgeable about sustainability, a significant gap remains between their stated intentions to purchase sustainable apparel and their actual buying behaviour. This paper aims to explore factors influencing purchase intention and barriers to actual purchase by using an extended theory of planned behaviour (TPB) and assessing perceived risks (APR). A quantitative research approach was employed, analysing survey data from 256 young urban Vietnamese consumers using structural equation modelling (SEM). The findings indicate that positive attitudes towards sustainable fashion, subjective norms, and sustainability concerns increase purchase intention, whereas perceived behavioural control does not. Moreover, perceived economic risk negatively affects the intention-behaviour relation, while perceived aesthetic risk has no significant effect. These insights offer the need for fashion retailers to address economic concerns through competitive pricing strategies, transparent value communication, and emphasising the long-term benefits of sustainable fashion.