Acid sulfate paddy soil is one of the problem soils in Guangdnng province. This study deals with the general properties of sulfur chemistry of acid sulfate paddy soils in Guangdong province. The minerals of lightly yellow mottles in acid sulfate paddy soils were analysed and identified with X-ray diffraction, and the total S, water soluble S, exchangable S, pyrite, jarosite, organic S, etc. were estimated. The data obtained showed that the S in acid sulfate soils was mostly in inorganic forms and dominated by pyrite (FeS₂). The.soils was getting acid mainly due to the oxidation of pyrite in the process of reclamation and drainage of man-grove swamp. With the planting rice by periodical irrigation-drainage, the oxidation of pyrite.and formation and hydrolysis of jarosite in the soil were promoted, resulting the decrease of pyrite and the jarosite going downwards gradually in the profile, all these facts indicate that the form, distribution and amount of S compounds, espeically pyrite and jarosite, in soil are,closely related with the developmant of the acid sulfate soils. Therefore, it is suggested that the chemical properties of S in the soil could be used as an indicator in identification and classification of acid sulfate soils.