Single-phase anorthite porous ceramics were in-situ prepared by a foam gel-casting method with CaCO3, α-Al2O3 and SiO2 as raw materials and environmental-friendly gelatin as a gel. The influence of gelatin amount on the phase composition, microstructure and properties (i.e., porosity, density, compressive strength, and thermal conductivity) of the samples was investigated. The amount of gelatin has no effect on the phase composition of the prepared material, but it affects the properties. The total porosity decreases from 89.7% to 88.0%, the bulk density increases from 0.28 g/cm3 to 0.33 g/cm3, the compressive strength increases from 1.02 MPa to 2.54 MPa, and the thermal conductivity increases from 0.038 W/(m·K) to 0.059 W/(m·K) as the gelatin amount increases from 6% to 12%. It is indicated that porous anothite ceramics with a low density, a high strength and a low thermal conductivity could be prepared by this promising method.