Disclosed is a method of producing an elliptic core optical fiber, in which a original preform having a circular core disposed at the center of a circular clad is processed to flatten on its periphery to form a processed preform that is then drawn with heating into an elliptic core optical fiber.According to the invention, the form of the processed preform used for producing an elliptic core optical fiber with desired specific dimensions can be designed using pre-obtained correlations based on the dimensions of the elliptic core optical fiber. If the processed preform designed like this is drawn with heating, an elliptic core optical fiber with desired specific dimensions can be reliably and easily produced.