The purpose of this study is to clarify land improvement method of early collective housing sites developed by Japan housing corporation during 1960’s-70’s constructed on marshland on Nakagawa lowland in Saitama prefecture - Misato, Yoshikawa, Takesato, and Soka-Matsubara. Those housings are mainly larger scale mid-rise buildings located on Tokyo suburbs and former land-use is paddy field where collective housings had been never built before 1950’s since those areas have deep alluvial layer. Through researching original construction drawings including boring survey data archived by UR, qualitative and quantitative value of the land improvement is evaluated. Many collective housing sites have been improved by soft-ground stabilization such as paper drain method and had earth fill up to higher level than flooding. Additionally, in order to construct more than five stories buildings, long piles were driven reaching support layer under the alluvial layer, which means each building footprint has necessary land strength. As landscaping, additional earthworks have been implemented to keep necessary soil depth for tree planting in open spaces. It is considered that development of a collective housing with larger scale at same time on marshland means to form sustainable ground keeping high capability as a living environment with rich planting foundation.