Provided are group-III nitride nanoparticles that prevent the piezoelectric field caused by strains on the nanoparticles, achieving good luminous efficiency. The group-III nitride nanoparticle represented by AlxGayInzN (0≤x, y, z≤1) incorporating two crystal structures; a wurtzite structure and a zincblende structure, in a single particle. As another example, the group-III nitride nanoparticle has a core-shell structure with a core and a shell, in which the particle constituting the core contains two crystal structures; the wurtzite structure and the zincblende structure, in the particle. Nanoparticles containing the two crystal structures can be produced by using a phosphorus-containing solvent as a reaction solvent, and the mixture ratio of the two crystal structures, (wurtzite structure)/(zincblende structure), is 20/80 or higher.