We prepared Ruddlesden+Popper-type layered perovskites Ca 2+x Sr x MnO 4 (x ؍ 0+2.0 at 0.25 intervals). Their precise crystal structures at room temperature and at 10 K were determined from both the X-ray and the neutron di4raction measurements. The compounds for x ؍ 0 and 0.25 have a tetragonal system with the space group I4 1 /acd (No. 142). The compounds for x ؍ 0.5}2.0 have a tetragonal system with the space group I4/mmm (No. 139). Magnetic susceptibility measurements have been performed for all the compounds in the temperature range between 5 and 350 K. The temperature-dependent magnetic susceptibilities were measured under zero-5eld-cooled (ZFC) and 5eld-cooled (FC) conditions at an applied 5eld of 1000 G. A dramatic di4erence in magnetic susceptibilities between ZFC and FC was observed below the Ne2 el temperatures for Ca 2 MnO 4 and Ca 1.75 Sr 0.25 MnO 4 , which shows the onset of a ferromagnetic moment below these temperatures. This moment is caused by the Dzyaloshinsky+Moriya interaction. Magnetic structures of Ca 2+x Sr x MnO 4 (x ؍ 0.0, 0.5, 1.0, and 1.5) solid solutions at 10 K have been determined by the neutron di4raction measurements. The nearest-neighbor Mn 4؉ ions are coupled antiferromagnetically in the (001) planes and the spins are parallel to the c axis.