Due to the recent economic development, the diet style has become more and more westernized in Korea, which increased the concern of our well-beings. Our well-beings are also associated with the gut microbiota which vary depending on the dietary intake. In this study, we compared gut microbiome shifted by two diets: high-fat diets (HFD) and low-fiber diet (LFD) based on 16S rRNA gene sequences using MiSeq. Compared to the control diet, LFD and HFD treatments significantly decreased species richness, while there was no difference in species evenness. Both diet treatments significantly increased the relative abundance of the Proteobacteria (p <0.05), especially the genus Sutterella. Bacteroidetes was significantly decreased in HFD groups, where the family S24-7 was decreased most. On the other hand, significant difference between HFD and LFD was seen among Firmicutes, where the abundance of family Lachnospiraceae was lower in LFD groups (p <0.05). PICRUSt-based metabolic difference analyses showed LFD treatment significantly decreased metabolisms of amino acid, carbohydrate and methane (p <0.01). In contrast, HFD significantly increased amino acid metabolism (p <0.05). Glycan biosynthesis and metabolism were significantly increased in both treatment groups (p <0.01). Our results suggest that longterm unbalanced dietary intakes induce gut dysbiosis, leading to metabolic and colonic disorders.