The object of the present invention is to provide a dielectric thin film and a capacitance element having excellent dielectric property.A dielectric thin film comprising a main component comprised of an oxynitride expressed by a compositional formula of AaBbOoNn (a+b+o+n=5), wherein said “A” is one or more selected from the group consisting of Sr, Ba, Ca, La, Ce, Pr, Nd, and Na, said “B” is one or more selected from the group consisting of Ta, Nb, Ti, and W, and crystalline particles constituting said dielectric thin film are polycrystalline which are not aligned to a particular crystal plane orientation, and a size of a crystallite of the crystalline particles included in the dielectric thin film is 100 nm or less.