The impact of rapid industrialization and urbanization on soil resources and the environment has been increasing in the Yangtze delta area over the past 20 years. More and more natural soils have been occupied by urban uses in many cities like Nanjing and original soil distribution patterns have been changed greatly. Studying and analyzing soil composition and nestedness helps to understand the distribution of pedotaxa better, estimate the aftermath of urbanization more accurately, and indicate further theoretical and practical implications in protecting soil resources and pedodiversity. Soil composition and nestedness of 70 town level units in Nanjing were analyzed with a software tool called Nestedness Temperature Calculator (Version Nov 1998). Results show that in Nanjing there are 47 pedotaxa types grouped into four classes; superior, common, rare and endangered with 6, 13, 25 and 3 members respectively. Pedological assemblages show the existence of an incomplete nested pattern, in other words, most pedotaxa present in the less rich sites are also present in more rich sites. A power law fit is satisfactory for a pedotaxa(S)-area(A) relationship in Nanjing and is S＝0.7284A^0.5922. Thus, in Nanjing there exist taxa-area positive correlations. Area size, landform type, as well as geographical position are considered to be the main factors forming the nested pattern. The town level units with larger area have more pedotaxa types due to the wider habitat range and more habitat diversity (such as water or landform conditions). As the area reduces, some habitat types are gradually lost, and the related pedotaxa type decrease produces the observed nested pattern.