The present invention provides a method of manufacturing Group III nitride crystals that are of high quality, are manufactured highly efficiently, and are useful and usable as a substrate that is used in semiconductor manufacturing processes. The method of manufacturing Group III nitride crystals includes: forming a first layer made of a semiconductor that is expressed by a composition formula of AlsGatIn1-s-tN (where 0nullsnull1, 0nulltnull1, and snulltnull1); forming a second layer by bringing the surface of the first layer into contact with a melt in an atmosphere including nitrogen, wherein the second layer includes greater defects in a crystal structure, such as a dislocation density for example, than those of the first layer, and the melt includes alkali metal and at least one Group III element selected from the group consisting of gallium, aluminum, and indium; and forming a third layer through crystal growth in the melt in an atmosphere including nitrogen, wherein the third layer is made of a semiconductor that is expressed by a composition formula of AluGavIn1-u-vN (where 0nullunull1, 0nullvnull1, and unullvnull1), and the third layer has less defects in a crystal structure, such as a dislocation density for example, than those of the second layer.