In the plow layer (0-20cm) of well drained low activity clay soils (mostly Oxisols and Ultisols) under "Cwa" tropical climate and long term cropped with cotton (42 sites) or sugarcane (45 sites), organic matter (y) was found to be similarly and highly related to soil texture. Best relations were found with clay (<2µ) plus silt (2-20µ) contents (x); (y = 0.773 + 0.0325x; r = 0.810***). A classification of soil organic matter contents, into low, medium and high levels, with different values for four major textural Classes is suggested. Ranges of medium levels of organic matter suggested were: 0.6 to 1.2% for sand and sandy loam; 1.0 to 1.8% for sandy loam and sandy clay loam; 1.5 to 2.8% for sandy clay and clay; 2.4 to 3.8% for heavy clay.