The study examines multi-unit residential building density in commercial zones of eight major Japanese cities, employing kernel density estimation with housing point data. Identified areas with over 4 housing buildings/ha in these cities reveal a broader prevalence of dense residential zones compared to Tokyo's central areas. Some cities exhibit high-density residential zones in areas with a floor area ratio (FAR) surpassing 700%.The findings propose a reevaluation of zoning practices, considering the concentration of multi-unit residential buildings in zones originally intended for commercial or business purposes.