Although modern society is more inclined to view authenticity from a postmodernist perspective, few quantitative studies on heritage tourism explored existential authenticity in detail. This study deconstructs authenticity into three components - object-related, intra-personal, and inter-personal - and then constructs a complete model by exploring each component's internal structures, asking to what extent travel motivation is an antecedent and loyalty, a consequence. Data were obtained from 1,088 valid survey questionnaires distributed in Pingxi, Taiwan. Study findings confirmed the reliability and validity of the items used to measure the construct of authenticity. Regarding the internal structure of authenticity, intra-personal authenticity plays a mediating role between object-related authenticity and inter-personal authenticity, and this inter-personal authenticity may be the final value that tourists perceive. Compared with recent related studies, this model more comprehensively explains the degree of variation in loyalty, reflecting its importance for heritage tourism management and marketing. If a destination remains authentic, tourists are willing make a return visit. Authenticity may enable tourism managers to strike a balance between preservation and development when achieving the long-term goal of sustainable development.