Abstract: Imperceptibility, robustness, security and hiding capacity are important indexes in evaluating information hiding algorithms. Recently, in most case, only imperceptibility and robustness were considered rather than the security ability. The later one is highly required to guarantee secret communication. With fully consideration of this requirement, one kind of hiding information algorithm is proposed based on run length, the main idea of which is to separate the image into several binary images first. Then according to the parities of the run length of the binary images, one bit of information can be successfully embedded while no more than one pixel that located along black-white boundary of the binary image is modified. The blind extraction of the hiding information can be achieved. The algorithm neither obviously changes of distribution property of 0 and 1 in image’s low plane, nor reduces the number of long run length. Hence it can successfully defend various detections that against Least Significant Bit (LSB) algorithm and improved LSB algorithm and it can also be applied in secret communication and other situations which require high security and large capacity.