Abstract: Yunnan brown coals with different moisture contents were prepared by vacuum-drying and thermostatic and humidistatic treatment, and the effects of moisture on the rheological behavior of brown coal-oil slurries were studied at atmospheric pressure and room temperature(t=19.3 ℃, p=1.01×10⁵ Pa). It is found that the moisture contents in raw coals have influences on the rheological properties of brown coal-oil slurries. The viscosity of the slurry decreases first and then increases with the increase in moisture. The moisture content ω_min at which the lowest viscosity occurs varies with shear rates and coal loadings. ω_min is 9.20% at the shear stress less than 4.4 s^-1 and 7.80% at the shear stress greater than 4.4 s^-1 as the coal concentration is 45.45%. ω_min becomes 7.40% at the shear stress less than 1.32 s^-1 and 10.00% at the shear stress greater than 1.32 s^-1 as the coal concentration is 55.56%. The thixotropy of brown coal-oil slurries is different for different moisture contents, and is enhanced with the decrease in the moisture contents. Brown coal-oil slurries containing moisture of various contents are pseudoplastic fluid, and the moisture contents also have some effects on the parameters of the rheological model.