Phenanthrene (PHE) is a constituent of Polycyclic Aromatic Hydrocarbon (PAH), considered as one of the most abundant marine pollutants with an organic root. It is mainly derived from pyrogenic and petrogenic sources. The aim of this study was to investigate the histological changes in gill’s structure of marine cultured tilapia fish larvae (Oreochromis spilurus). The larvae of the tilapia were ingested to phenanthrene mixed with fish food, they were fed twice a day for 14 days, the experiment was terminated on Day 14. The effect of phenanthrene on the gill’s structure was noticed and compared to the control group. As a result, there were noticeable histological changes on gills after treatment including, hypertrophy and fusion of the secondary lamellae. The mucus cell numbers in gill’s sections was increased in the treated group with 100 mg L-1 of phenanthrene until the termination of the experiment. Overall, the deleterious effect of phenanthrene on gills histology was evidence at 100 mg L-1 and further studies are recommended to study the histological effects of phenanthrene on other tissues of the tilapia fish.