Abstract We have investigated the reversible magnetization M(T,H) of YBaCuO ceramics. The three superconducting phases of this system (Y-123: YBa 2Cu 3O 7; Y-247: Y 2Ba 4Cu 7O 15 and Y-124: YBa 2Cu 4O 8) present a small reversible regime below T c extending over 10 to 25 K, depending on the external magnetic field (3 to 55 kOe, respectively). Within these temperature and field limits, the magnetization can be described satisfactorily by the London model. Using additionally the Werthamer-Helfand-Hohenberg (WHH) temperature dependence for H c2(T) and the 2-fluid parabolic law for H c(T), a fit of all reversible data yields μ o∂ H c2,c/∂ T| Tc≈−4.3 T/ K, ξ ab(0)≈10.8 A ̊ and λ ab(0)≈1650 A ̊ for the Y-123 phase. The critical field appears to be significantly higher than that obtained by other methods. Lower critical fields are obtained for Y-124, and intermediate values are found for Y-247, as expected from its crystallographic structure that consists of alternating blocks of Y-123 and Y-124.