To provide a fluorescent colloidal solution which gives a great luminescence at a low exitation energy, is good in producibility, and is excellent in light transmission; a fluorescent fine particle contained in the same; and a fluorescence thin film using the same.

The fluorescent colloidal solution comprises a fluorescent fine particle and a solvent dispersing the particle, wherein the fluorescent fine particle is a metal sulfide which is doped with an activator and has an average particle size of 1-10 nm, and the colloidal solution at a concentration of 10% gives a transmission of 50% or more for a visible ray measured by a spectrophotometer.