Superconductivity was observed in SrPd2Sb2 polymorphs: a primitive tetragonal CaBe2Ge2-type (low-temperature phase, LT-SrPd2Sb2) structure and body-centered ThCr2Si2-type (high-temperature phase, HT-SrPd2Sb2) structure. The superconducting transition was observed at T-c = 1.95 (LT) and 0.6K (HT). The specific heat C(T) showed a clear anomaly at T-c = 1.85 (LT) and 0.6K (HT); thus, the superconductivity was of a bulk nature. The agreement with the Bardeen-Cooper-Schrieffer (BCS) curve indicated that the LT-SrPd2Sb2 superconductor was fully gapped. The values of electron-phonon coupling lambda(ep) and density of state at Fermi level N(E-F) in 122 compounds with the CaBe2Ge2-type and its related structure were evaluated to reveal the main factor that determines T-c. From our systematic analysis, T-c of this family can be explained by lambda(ep) rather than N(E-F).