We suggest a cast Alnico magnet as a new microwave absorber. The proposed Alnico microwave absorber shows advanced microwave absorption properties of 24 ㏈ at 13.3 ㎓ for the thicknesses of 1 ㎜. We also investigated the effects of the carbon, which effects strongly to microwave absorption in Alnico magnet microwave absorbers. Central frequency shifts toward lower frequency with increasing Alnico content which is related to the frequency to show tanδ>1. Also, we investigated the sample thickness dependence on the microwave absorption properties.