Abstract: A study on diversity and distribution of fish communities and water qualities were carried out from January 2009 to December 2010 to cover monsoon and non-monsoon at Kuantan estuary, Pahang, Malaysia. A total of 19 species of primary marine fish belong to 12 families were recorded. Out of 311 individuals the fish fauna was dominated by Ariidae followed by Lutjanidae and Lactaridae. As such Ariidae contributes 50% of the fish caught in the study area and its diversity index (H’) was 0.97. A The Ariidae family consist of four (4) species; Arius maculatus, Arius sumatranus, Arius tenuispinis and Arius thalassinus. The Ariidae family can be found in all stations as they are euryhaline (highly tolerant to salinity) and this fish family are known to be a hardy estuarine catfish. Among all species in family Ariidae, Arius thalassinus was the most dominant (23%) among all species. As such collected species showed highest species diversity (0.34) followed by Arius tenuispinis (0.25) compared to other species. Arius tenuispinis alone contributed 11.90% among the samples caught from all stations. The fishes were caught and recorded highest in September-December. Pseudorhombus quinque ocellatus, Nibea soldado, Sardinella fimbriata, Toxotes jaculatrix, Dasyatis ushiei, Setipinna taty were the least dominant in the Kuantan estuary with 9.33% of total abundance. Physico-temperatures, such as temperature (22.03-30°C), Conductivity (10.342.43 mS cm-1), TDS (0.06-26.34 mg L-1), salinity (0.05-29.09 ppt), DO (6.37-8.38 mg L-1), pH (4.97-8.03), Chl a (0.01-1.33 μg L-1), nitrite (0.01-0.08 mg L-1), nitrate (0.60-0.88 mg L-1), phosphate (0.24-0.40 mg L-1). Nevertheless, the study envisages that the water quality and fish diversity are still conducive in the Kuantan estuary. The fish diversity of Pahang estuary was high monsoon compared to non-monsoons. The station 4 (LKIM fishing boat jetty and adjacent Hospital Kuantan) is the most polluted area due to the presence of several outskirts could be alarming for the sustainable development of fish and other aquatic organisms in Kuantan estuary in the long run.