Intertidal epilithic microalgae play very important role as feed of higher organisms. Taxonomical composition of epilithic algae and their seasonal dynamics in relation with environmental factors were studied at middle coast of Saudi Arabia, namely Yanbu, Ar-Rayis, Mastorah, Rabigh and Thuwal, the Red Sea. Temperature, salinity and pH varied from 22.10-32.02°C, 38.72-39.35 psu, and 8.40-8.63, respectively throughout the study. A total of 87 epilithic microalgal species belonging to 4 families was identified: 79 Bacillariophyceae, 5 Cyanophyceae, 2 Dinophyceae, and 1 Cryptophyceae. The epilithic microalgal abundance varied from 2.32 × 105 cells/L to 7.66 × 105 cells/L during the study with an average of 4.03 × 105 cells/L. The lowest and highest abundance of epilithic microalgae occurred in winter and summer at Mastorah and Rabigh, respectively. Among the microalgae taxa, diatoms were the dominant group which was 91.01%, followed by Cyanophyceae (5.62%), Dinophyceae (2.25%) and Raphidophyceae (1.12%). Among diatom, the centric and pennate diatoms were 74.07% and 25.93%, respectively throughout the study. The occurrence frequency analysis revealed that high frequently observed epilithic microalgae were Licmophora flabellata, L. paradoxa, L. remulus, Navicula vula, N. incerta and N. transitans throughout the study. Therefore, it could be said that diatoms are the major group of epilithic microalgae which show high abundant in summer at the northwest coast of Jeddah, Saudi Arabia, the Red Sea. Second dominant group was Cyanophyceae, and the dominant species was Spirulina subsalsa among epilithic microalgal community.