Results of a creep study conducted on hollow cylindrical microconcrete specimens in compression and torsion, at 50 and 100% relative humidity, are presented. Most of these specimens were subjected to a sustained load for 37 days at 73°F (23°C), and then heated to 140°F (60°C) or exposed to thermal cycles between 73 and 140°F (23 and 60°C). Also presented is a mathematical expression, developed in terms of material parameters and functions, for predicting creep of concrete. The expression is based on the thermodynamic equilibrium of the diffusible load-bearing layers in the cement gel, taking into account temperature, humidity, age and type of load. Calculated creep values, using the mathematical expression, compared well with the experimental results.