NOVELTY - A transparent substrate has a base material (12) containing transparent thermoplastic polyimide and an inorganic filler. The refractive index difference of transparent thermoplastic polyimide and inorganic filler at wavelength of 589 nm is 0.01 or less.    USE - Transparent substrate is used for display panel of image display apparatus (claimed). Uses include but are not limited to liquid crystal display element, organic electroluminescent display element, flexible display, touch panel, solar cell substrate, optical lens, optical element, etc.    ADVANTAGE - The transparent substrate has high transparency, heat resistance and flexibility. The transparent substrate is formed using polyimide composition having high transparency and refractive index.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) manufacture of transparent substrate, which involves impregnating inorganic filler into polyamic acid, imidating polyamic acid, heat-processing, obtaining base material containing transparent thermoplastic polyimide, laminating film containing polyimide and which does not contain inorganic filler on surface of base material, and heat-fusing base material and film;    (2) transparent polyimide composition, which contains mixture of polyimide containing structural unit (a) of formula (I), polyimide containing structural unit (b) of formula (II), or a polyimide copolymer including structural unit (a) and structural unit (b). The refractive index of polyimide having structural unit (a) at 589 nm is 1.59-1.65. The refractive index of polyimide having structural unit (b) at 589 nm is 1.52-1.55. The refractive index of thermoplastic polyimide composition at 589 nm is 1.53-1.62; and    (3) polyamic acid composition, which contains mixture of polyamic acid containing structural unit of formula (III), polyamic acid containing structural unit of formula (IV), or polyamic acid copolymer containing structural units (III,IV).    X,Y'=tetravalent organic group.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of transparent substrate.    Base material (12)    Layers (14,14')