The strength of sintered low-temperature co-fired ceramic (LTCC) disks was measured under dry (< 2% relative humidity [RH]) and wet (98% RH) conditions, using ring-on-ring, biaxial-flexure testing in the stressing rate range of 0.002-2 MPa/s. The empirical sub-critical crack growth parameters, n and A, were calculated. The values of the parameters in the wet environment were higher than in the dry environment. It is argued that the high RH n value is more representative of material behavior. Results of fractographic examination are reported and expected lifetime and safe design stresses for LTCC are calculated.