In an ultrafine ZnO particle dispersion, ultrafine ZnO particles are dispersed and float in a hydrophobic solvent while being surrounded by a surfactant composed of a primary surfactants such as polyoxyethylene nonylphenyl ether, and a secondary surfactant such as 1-octanol. The ultrafine ZnO particles have an average particle diameter D50 of 10 nm or less and a ratio of the standard deviation σ to the average particle diameter D50, σ/D50, of 0.2 or less. The average particle diameter D50 of the ultrafine ZnO particles can be controlled by changing the side chain length of the hydrophilic group of the primary surfactant. A ZnO thin film produced by using this dispersion solution has a ratio of a maximum emission intensity in a visible region to a maximum emission intensity in a ultraviolet region, P1/P2, of 0.2 or less. Thereby, an ultrafine ZnO particle dispersion solution in which ultrafine ZnO particles having a very narrow width of particle size distribution and being in nanometer level with an average particle diameter of 10 nm or less are present in a monodispersed state, and a ZnO thin film produced by using this are realized.
