Understanding the determinants of rhino horn prices in an illegal market will facilitate designing policies to conserve wild rhinoceros. Using a general theoretical model, we identify empirical measures that may affect the illegal market price of rhino horn and derive testable hypotheses about the effect of these measures on the price. To test these hypotheses, we conduct a first-ever analysis of the determinants of the actual illegal market price of rhino horn using time se-ries data. Price data were collected from consumers who had purchased rhino horn in Vietnam from 2001 to 2020. We find that China's legalisation of the trade in rhino horn antiques and implementation of an anti-corruption campaign significantly reduced the illegal price. Thus, our findings suggest that aggressive institutional reforms and broad governance crackdowns, as an alternative to wildlife-specific policies, can disrupt illegal markets for endangered wildlife prod-ucts. We also recommend that restrictions on the legal supply should be combined with de-mand-side measures to effectively influence the consumption of illegal rhino horn.