In situ neutron diffraction measurements of two low-alloy steels and a 304-type stainless steel during tensile and creep tests were performed at room temperature. Changes in the diffraction pattern, the integrated peak intensities of austenite (gamma), and the peak positions of gamma were analyzed and discussed to elucidate the relationship between intergranular stress in gamma and the occurrence of martensitic transformation during deformation. Tensile loading experiments revealed that the susceptibility to martensitic transformation depended on the gamma-(hkl) grains, where gamma-(111) grains underwent martensitic transformation at the latest. The volume fractions of gamma were found to decrease under an applied load but to remain almost unchanged under constant load in creep tests, where the lattice strains of gamma-(hkl) grains were mostly unchanged. The gamma-hkl dependence of the susceptibility to martensitic transformation was found to be controlled by the shear stress levels in gamma-(hkl) grains, which were affected by the intergranular stress partitioning during deformation.