Abstract: The present invention relates to a bag for a laptop computer with a shape improved so as to adjust its size. The size adjustable bag for a laptop computer according to the present invention includes a support for supporting a laptop computer, side covers for covering side portions of the laptop computer, an upper cover for covering an upper portion of the laptop computer, a lower cover for covering a lower portion of the laptop computer, a shock absorbing material inserted between an outer fabric and an inner fabric of the respective covers, at least one Velcro fastener attached onto an inside of the upper cover, inside and outside of the side covers and an outside of the lower cover, from a right end to a left end of the respective covers, and at least one seam line with size adjusting function formed at lower peripheries of the respective covers.