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Cellular materials with ultralow density (e.g., < 5 mg cm−3) are attractive candidates for acoustic applications due to their lightweight and other unique properties. However, it has remained a challenge to fabricate such materials. Here, we synthesized a series of graphene-based cellular monoliths (GMs) with densities from 4.01 to 0.82 mg cm−3 using a facile and cost-effective freeze-casting procedure. The sound absorption behaviors of the ultralight GMs were explored, and the results demonstrate that the GMs with a density over 2.24 mg cm−3 could effectively dissipate the incident sound wave energy with the sound absorption coefficient > 0.8 in a broad frequency of ranges. Together with their high mechanical stability, fire retardancy and thermal insulation capability, GMs may find applications in the domestic, industrial and defence areas. [ABSTRACT FROM AUTHOR]