Porous, spongy absorbers are considered to be the most promising candidates for lightweight and highly efficient microwave absorption material. However, conventional sponges or foams reported previously are difficult to meet the high performance requirements. Here, a lightweight (42 mg/cm³), porous CNT@TiO₂ sponge with core-shell structure CNT/TiO₂ was successfully prepared via a simple combination of hydrolysis and heat treatment method. In the sponge, the thickness and crystal structure of the TiO₂ shell layer, and the mass fraction of TiO₂ and CNTs can be precisely controlled by the growth processes, resulting in adjustable dielectric loss properties of the samples. With the optimized component proportion, it was found that a minimum reflection loss value of −31.8 dB was observed at 10.35 GHz, and reflection loss exceeds −10 dB is up to 2.76 GHz for the absorber with the thickness of 2 mm. Moreover, the effective microwave absorption (<10 dB) can be achieved in the range of 3.43–12.0 GHz by adjusting the thickness of the absorber. These results indicate that the CNT@TiO₂ sponges can serve as attractive candidate materials for lightweight microwave absorption materials.