An optical waveguide having a core for light transmission therethrough, wherein the core is made of a polyimide copolymer including at least two units represented by the formulae [II]and [III] as follows: ##STR9## wherein each of R1 and R2 is a tetravelent organic group selected from the group consisting of ##STR10## with the proviso that R1 and R2 are different from each other.