Determination of diel variations of fish assemblages around artificial reefs may provide a better understanding of the ecological and biological process occurring in these man-made structures, as well as more accurate evaluation of their effectiveness. The aim of this study was to determine the diel variations of the fish assemblages on artificial reefs on muddy and sea grass meadow areas of Western coast of Turkey (Aegean Sea). To determine the diel variations, visual census were conducted according to a time schedule (06:00-07:00, 12:00-13:00, 18:00-19:00 and 24:00-01:00) by SCUBA divers in August 2004. Counts were made as three replicates during each time period. A total of 27 fish species belonging to 10 families were recorded in DAR. At GUAR, 27 fish species belonging to 13 families were recorded. The lowest species (3 in both sites) and individual numbers (4 in GUAR and 9 in DAR) were recorded at night (24:00-01:00 period) observations in both sites while the highest numbers were recorded at 06:00-07:00 at DAR (16 species and 838 individuals) and at 12:0013:00 at GUAR (11 species and 1068 individuals). Biomass values changed between 293 g and 20,600 g in DAR. The lowest value recorded at night and highest value at 12:00-13:00 period. In GUAR, the lowest and the highest values were recorded during morning observations. In result of study, it was found that fish assemblages showed significant diel variations in both environments.