Abstract: We have presented here a study on the characteristics of a photochemical pollution episode in Hong Kong during Mar.28th-Mar.31th, 2000. In this episode, the maximum concentrations of O₃, NO₂, CO, RSP, SO₂ reach 175.2 μg/m³, 333.5μg/m³, 5405 μg/m³, 349.3 μg/m³ and 132.8μg/m³, respectively. The episode lasts three days in areas of urban Hong Kong. The synchronous meteorological data and air monitoring data are adopted for the analysis with focuses on concentration variation, meteorological pattern, the mechanisms of local photochemical pollution and regional transport. Investigations have revealed the principal characteristics of this episode. The possible reasons can be that clear sky with high temperature and low humidity as well as local emissions are attributable to the episode. Also, regional transport plays an important role on the episode. It indicates that the geographical location, urban building and traffic status of Hong Kong are beneficial to the formation of photochemical pollution.