Variables such as richness, diversity, evenness, relative abundance (RA), and sighting frequency (SF) were assessed in order to characterize reef fish assemblages in Santa Marta and Tayrona Natural National Park (TNNP). The effect of the TNNP protection on these attributes was evaluated. Data were registered in 20 sites by means of the roving diver in diversity and evenness between zones (p< 0.05) indicating a TNNP protection effect, but not differences in richness. Species composition was moderately similar between the two zones (Jaccard Index 0.69). Nevertheless, families such as Serranidae, Haemulidae, and Lutjanidae showed differences in species composition between evaluated zones. Large groupers and snappers exhibited RA and SF considerably low at both protected and not protected zones. Differences were only recorded between small body size and non-target species. These results suggest that the TNNP can be facilitating the preservation of high species diversity, but fishing control systems should be more efficient in order to promote protection and conservation of more vulnerable reef fish populations (snappers and groupers).