A design method for an optical sheet for solar concentration and an optical sheet for solar concentration obtained by means of the design method are disclosed. The design method is characterized in that, for a resin optical sheet for solar concentration containing an ultraviolet absorber in a base material thereof, an amount of the ultraviolet absorber to be contained in the base material is determined such that: in an accelerated degradation test by means of a metal-halide-lamp weathering test (device specification: JTM G 01:2000, Japan Testing Machinery Association), decrease in average transmittance in a wavelength range of 400 nm to 1850 nm after testing for an irradiation time T1 satisfies the following equation (1) τuv(0)+τuv(T1)>τ0(0)+τ0(T1)   (1) and that decrease in transmittance at each of wavelengths in the wavelength range from a corresponding initial value after testing for the irradiation time T1 is not greater than 10%. T1 is the accelerated test time required corresponding to the actual location of use. The optical sheet of the present invention is capable of efficiently concentrating light without decrease in transmittance while being used for a long time in an environment with a large amount of ultraviolet radiation.