Hydroperfluorocarboxylic acids (H-PFCAs) have attracted worldwide attention for their potential use as alternatives to perfluorocarboxylic acids (PFCAs). Decomposition of these chemicals is of great significance due to their possible environmental risks. In this work, the photodegradation of typical H-PFCAs (HCnF2nCOOH, n=4, 6, 10) in water by a 500W mercury lamp was systematically examined. We found that the photodegradation of H-PFCAs all followed pseudo-first-order kinetics, and the photoreactivity increased with carbon chain length. The degradation pseudo-first-order rate coefficients of H-PFCAs were slightly slower than the corresponding PFCAs. The decomposition efficiency of HC10F2COOH was enhanced by lowering pH, but inhibited by the presence of humic acid. Three common inorganic ions showed inhibitory effect on HC10F2COOH photodegradation, with the order of NO3- > CO32- > HCO3-. This is because these anions have different light absorption, making less light available for compound degradation. As a photosensitizer, Fe3+ had an obvious promoting effect on the reaction. According to the products identified by mass spectrometry analysis, decarboxylation, defluorination and elimination reaction were mainly involved in the photodegradation of HC10F2COOH. Toxicity predictions by ECOSAR program showed that photolysis can reduce the aquatic toxicity of HC10F2COOH. This work could provide useful information for developing a simple and effective technology to treat H-PFCAs in water.