In this paper we reviewed the importance issues of the optical character recognition, gives more emphases for OCR and its phases. We discuss the main characteristics of Arabic language, furthermore it focused on the pre-processing phase of the character recognition system. We described and implemented the algorithms of binarization, dots removing and thinning which will be used for feature extraction phase. The algorithms are tested using 47,988 isolated character sample taken from SUST/ ALT dataset and achieved better results. The pre-processing phase developed by using MATLAB software.