A soil development index was developed to quantitatively measure the degree of paleosol development. This index combined paleopedogenic features with ten soil macro- and micro-morphological properties from morphological descriptions of Potou and Jiu Zhoutai loess sections in the Loess Plateau of China. Description of the micromorphological properties was based on 187 thin sections. These ten morphological properties are: rubification (color hue and chroma), total texture (texture type, stickiness and plasticity), melanization (color value), microstructure (type, grade of pedality, total porosity and void types), fine material (abundance), primary carbonate (abundance), biotite (abundance and degree of alteration), Fe(hydr) oxides (abundance), secondary carbonate (micromorphology type and abundance) and illuvial clay (interference colors, lamination features, abundance and thickness of clay film). Future study may reject some of these properties and add others. The index was preliminarily tried to the field of paleoenvironmental research. The index works well with the loess-paleosol sequences, successfully identifying paleosols and weak-paleosols from a loess-paleosol sequence.