The present invention provides an improved card adapter structure that includes an upper cover, a lower cover, a converter terminal set and a positioning elastic strip set. The upper cover has a structure designed to conform to short memory card (MS) specifications, wherein an insertion slot is defined at the rear of the upper cover corresponding to the shape of a micro memory card (M2). The lower cover has a fixing portions and a positioning structure corresponding to those of the upper cover. Moreover, at least one terminal of the No. four, six, seven and eight terminals of the converter terminal set is configured with a gap that is joined to an electric resistance. The positioning elastic strip set is correspondingly located between both covers. Accordingly, the present invention is able to convert a micro memory card into a short memory card of relatively larger size.