The term flexo “post"-printing is used for printing on combined corrugated boards, as opposed to “pre"- printing of the liner board before assembling the corrugated board, (Martin H., 2007(, The low printing pressure and flexible printing plates make flexo the primary printing method for corrugated boards. This study aims to investigate the effect of using this flexo post-printing method toprint halftone Colored QR codes and QR codes colored with the main printing process colors (CMYK) which are the most famous colors used on corrugated boards packages in the Egyptian market, on the readability of these printed QR codes by Smartphone cameras that uses any suitable reader software. As a result of an experimental study, it has been proven that the very dark colored QR codes are very good to print on corrugated board because they can be read correctly from the first time because they make a very high contrast difference between them and the brown background (80% and more). Similarly halftone process colored QR codes can be printed on corrugated boards by regular flexo post- printing machines, and can be decoded correctly and very quickly by Smartphone cameras, provided that keeping the printing parameter like color registration in its high accuracy level for getting a high quality printed QR codes very close to the printed solid ones, and they should make at least 60% contrast difference between them and the brown corrugated board. On the other hand, colored QR codes that make a very low contrast difference with the background, and halftone process colored QR codes which make a slightly contrast difference with the brown background, ranging between 52% to 57% are not preferable to print, So finally, If you're going to colorize your QR code and print it on corrugated board package, make sure there is at least 60% contrast difference between the squares and the background, and keep color registration in its high accuracy level for getting a high quality printed QR codes very close to the printed solid ones.