The noble pen shell Pinna nobilis (Linnaeus, 1758) is the biggest bivalve of the Mediterranean Sea; its shells provide hard substrate for various epibionts. However, the researches of epibiontic comunities on pen shells are rare in the Adriatic. Therefore goals of this work were to determine the composition and structure of epibionts on pen shells from two locations in the Adriatic and to define their spatial variability based on species composition and surface area covered. Analysis of photographs revealed 35 epibiontic taxa in total on both stations. A higher taxa abundance was found inside Javorike bay (National Park Brijuni; 27) than in Malo Jezero (National Park Mljet; 17). Turf algae prevailed in epiflora of the both locations and polychaete worms (Serpulidae indet.) prevailed in epifauna. The spatial variability of epibiontic comunities was significant. In the regard to surface area covered, difference in abundance of turf algae contributed the most to variability while considering epibiontic composition red calcification algae contributed the most to variability between the locations. Literature survey yielded 331 epibiontic taxa that have been recorded up to now in the Mediterranean. This work presents the first quantification of epibionts on Pinna nobilis based on surface area covered in the Adratic region. Use of the same methodology in future researches would enable the direct comparison of the results, and thus would improve our knowledge about epibiontic comunities on the Pinna nobilis shells in the various geographical and environmental conditions.