Experiments were conducted to determine the relationship between the soil moisture content and the soil moisture tension. The work was done with four types of soil of the state of São Pauio: terra-roxa-legítima, massapê, arenito Bauru and arenito Botucatu. In each type of soil the 0-15; 15-30; 30-45; 45-70 and 70-100 layers were studied. The samples were wetted and were brought to the fallowing tension range: 0,1, 3, 8, 15 and 20 atmospheres. For each type of soil a characteristic moisture curve from the lower to the upper limit of moisture available to plants is presented. The curves show that the highest amount of the soil moisture available to plants is held under a tension below 8 atmospheres. It was observed that the moisture holding capacity of the soil depends largely upon its clay and organic matter content.