A study on stiffness degradation of glass fiber-reinforced composite laminates subjected to uniaxial tensile, pure torsional, and biaxial cyclic fatigue loading at cryogenic temperature is presented. The tensorial nature of stiffness change in the composite material is discussed first to establish a basis for fatigue experiments. Uniaxial tensile and pure torsional cryogenic fatigue tests were conducted to provide references for the study of more complicated multiaxial fatigue. Biaxial cryogenic fatigue under cyclic tension-torsion loading was then performed to examine the effect of complex states of cyclic stress. Stiffness deterioration in terms of changes of elastic constants during fatigue is studied for the cases of various loading conditions. The fundamental nature of cryogenic fatigue degradation in the composite material is investigated. Basic damage mechanisms and mechanics associated with the stiffness change during cyclic fatigue are discussed. Implications of the cyclic stiffness degradation on cryogenic fatigue failure and on the design and analysis of cryogenic composite structures and components are also discussed.