Using a sol-gel method, Nd1-xCaxFeO3 nanoparticles with nearly the same average particle size and different Ca contents (x=0.1–0.5) and Nd0.9 Ca0.1 FeO3 nanoparticles with different particle sizes were prepared. Crystal structure and magnetic properties for the Nd1-xCaxFeO3 (x=0.1–0.5) nanoparticles have been investigated by x-ray diffraction and magnetic measurements. Both series samples have orthorhombic perovskite structure and the space group Pbnm. The Nd(Ca) ions and O ions are displaced from the ideal cubic positions. The oxygen octahedra around the Fe ions are distorted. Both the increasing Ca content and the increasing particle size lead to a decrease in Fe–O bond length and an increase in Fe–O–Fe bond angle. Magnetic measurements show the existence of a weak ferromagnetism and the mainly antiferromagnetic ordering of the spins in the Nd1-xCaxFeO3 nanoparticles. The spontaneous magnetization of the weak ferromagnetism decreases with increasing Ca content or increasing particle size. The influence of structure on magnetic properties is discussed. © 2002 American Institute of Physics.