<p>Understanding the noncoaxial behavior of sands, especially under complex loading conditions, is an attractive topic for geotechnical engineering researchers. Noncoaxial behavior refers to the misalignment between the principal stress directions and the principal plastic strain rate during plastic deformation. In this study, the effect of particle shape and sphericity on the noncoaxial behavior of sands was investigated. To achieve this, experiments were conducted on sands with different particle shapes (Hamedan, Chamkhale, Firoozkuh, Leighton Buzzard, and Ottawa) using a hollow torsional cylinder apparatus. The samples were subjected to monotonic loading paths with principal stress angles of 15°, 30°, and 60° to evaluate the influence of principal stress direction variations on sand behavior. The results showed that particle shape and sphericity significantly affect the noncoaxial behavior of sands. Spherical particles exhibited less noncoaxial behavior compared to angular particles, while an increase in particle angularity led to a considerable rise in noncoaxiality. The angle of noncoaxiality exhibits the greatest variation in Hamedan sand (which has the lowest sphericity), with a change of approximately 20° at a loading angle of 60°, and the least variation in Ottawa sand (which has the highest sphericity), with a change of approximately 5° at a loading angle of 15°.</p>