The correlation between electrical and mechanical losses in ferroelectric ceramics has been investigated theoretically and experimentally. The theoretical derivation is based on the assumption that both loss types are induced by 90° domain walls moving under the influence of electrical or mechanical fields. A proportionality between both loss types is found. The factor of proportionality includes material constants such as spontaneous polarization and striction, permittivity, and elastic compliance, but is independent of the specific energy dissipation mechanism of a moving domain wall. In a compositional series of differently doped PLZT ceramics with a broad range of losses the theoretically derived relations have been checked experimentally. Good agreement between the experimental and theoretical results was found.