Abstract: To investigate the mineralization of farmyard manure in tobacco-planting soils, a well-rotten farmyard manure was made which contained corn straw and pig manure. An in-situ cultivation method with sand filter bags was applied to study the mineralization characteristics of organic carbon and organic nitrogen in the well-rotten farmyard manure and its effects on humus acid composition and the contents of available nitrogen, phosphorus and potassium in Ningnan tobacco-planting areas of Liangshan in Sichuan Province. The results showed that the mineralization rates of carbon and nitrogen in the manure were higher at the early stage of fertilizer application (within 30 days after burial). On the 60th day after burial, the mineralization rates of carbon and nitrogen were 65.13% and 46.26%, accounted for 80.07% and 92.39% of the total mineralization rates of carbon and nitrogen during the whole tobacco growth and development stage, respectively. There was no nitrogen supply peak 60 days after burial, which satisfied the tobacco fertilizer requirement of "pre-promotion and post-control". The farmyard manure maintained relatively higher contents of available nitrogen, phosphorus and potassium in soils to provide sufficient nutrients for the growth of flue-cured tobacco. Furthermore, farmyard manure promoted the formation and accumulation of humic acid (HA) and fulvic acid (FA) in soils, especially at the later stage of tobacco growth. It also significantly raised HA/FA ratio in soils and improved soil environment.