<p>Despite the reported paradox in Gen Z’s fashion consumption, research on their behavior within the coexisting sustainable and fast fashion markets remains limited. This study aims to investigate Gen Z college students’ fashion behavior by exploring the competitive coexistence of sustainable and fast fashion, employing a robust theoretical framework. An integrated research model combining the Theory of Planned Behavior (TPB) and the Value-Attitude-Behavior (VAB) framework is proposed to address the limitations of each approach. The model examines the hierarchical influence of personal values and attitudes toward sustainable and fast fashion on individual purchasing behavior while also exploring the impact of subjective norm (SN) and perceived behavioral control (PBC) on purchasing decisions for both sustainable and fast fashion. Structural equation modeling was used to test 14 hypotheses based on a dataset of 289 female Gen Z consumers. The results revealed values, attitudes, and perceived behavioral control play significant roles in both sustainable and fast fashion consumption, suggesting that different personal values lead to varying fashion behaviors. No significant attitude-behavior gap (e.g., ethically-minded consumers rarely purchasing ethically) was observed in sustainable fashion consumption, contrary to commonly reported findings. The relationship between sustainable and fast fashion consumption within Gen Z’s fashion market was also confirmed. Our findings enhance the understanding of Gen Z college students’ paradoxical purchasing behavior in relation to the major fashion retailers. The results help close the gap in sustainable fashion consumption research and offer valuable managerial insights.</p>