Synthetic conditions such as stoichiometries, temperature and pressure are optimized to achieve a high quality oxygen deficient SmFeAsO0.6 superconductor. Both electric and magnetic measurements show a sharp superconducting transition at about 55 K. Several important physical parameters are deduced. The apparent superconducting gap observed in heat capacity with 2 Delta(o)/k(B)T(c) of 4.57 larger than that of previous fluorine replaced samples indicate that this superconductivity will not strongly conflict with the phonon-mediated BCS mechanism. The mean free length l = 18.8 nm and the coherent length xi = 2.3-3.3 nm show that the superconductivity is in the clean limit. (C) 2009 Elsevier Ltd. All rights reserved.