Third-order optical non-linearities of CuCl microcrystallites with sizes of 6.8-11.0 nm in glasses were investigated. Absolute values of third-order non-linear susceptibilities, χ ( 3 )(-ω 1 : ω 1 , -ω 1 , ω 1 ) , were measured in the resonance region by a degenerate four-wave mixing method and χ ( 3 )(-ω 2 : ω 1 , -ω 1 ,ω 2 ) were measured in the near resonance region by a non-degenerate four-wave mixing method. χ ( 3 )(-ω 1 : ω 1 , -ω 1 , ω 1 ) was strongly dependent on the frequency, ω 1 , of incident beam, while χ ( 3 )(-ω 2 : ω 1 , -ω 1 , ω 2 ) was less dependent on the frequency, ω 2 , of incident beam under the resonant excitation condition. In the non-degenerate four-wave mixing configuration in which the pumping frequency is resonant with the confined excitons, the figure of merit, χ ( 3 ) /α, was enhanced to more than an order of magnitude compared with that in the degenerate four-wave mixing configuration in a near resonance region.