The < or =-process branching in the mass region 150< or =A< or =154, initiated by the /sup 151/Sm ..beta../sup -/ decay, is reinvestigated, particularly in connection with the solar /sup 152/Gd abundance. The Maxwellian averaged neutron caputre cross sections for kT = 25 keV are measured for /sup 152/Sm, /sup 151/Eu (to the 9.3 hour isomeric state of /sup 152/Eu), /sup 152/Gd, /sup 158/Gd, and /sup 160/Gd. The ..beta..-decay rates of the unstable nuclei involved in the branching are calculated theoretically. In addition, it is shown that the thermal equilibration between the ground state and the isomeric state in /sup 152/Eu under plausible s-process conditions is achieved on a time scale shorter than those for ..beta..-decay and neutron capture. With these results and the neutron capture cross sections from literature for the other concerned nuclei, a branching analysis is performed within the steady flow model of the s-process. This study yields constraints for s-process models, particularly with regard to temperature and neutron density.