Fusobacteria are associated with colorectal cancer (CRC) and are amplified during colorectal carcinogenesis. Compared to the adenoma-carcinoma sequence of carcinogenesis, serrated neoplasm has distinct clinical features and a different molecular background. We aimed to compare the gut microbiome between tubular adenoma (TA) and sessile serrated adenoma/polyp (SSA/P). Patients with TA, SSA/P, or CRC were recruited. Three pieces of colorectal mucosal tissue were obtained from each patient by endoscopic biopsy. 16S rRNA gene pyrosequencing and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were performed. Among 26 enrolled patients, 8, 10, and 8 had TA, SSA/P, and CRC, respectively. The relative abundance of Fusobacteria did not differ significantly between the TA and SSA/P groups (4.3% and 1.9%, P = 0.739) but was higher in the CRC group (33.8%) than in the TA or SSA/P group, respectively (TA vs. CRC, P = 0.002, false discovery rate [FDR] = 0.023; SSA/P vs. CRC, P < 0.001, FDR = 0.001). PICRUSt revealed that most functions in the TA metagenome were similar to those in the SSA/P metagenome. The gut microbiome, including relative abundance of Fusobacteria, did not differ between TA and SSA/P, suggesting that Fusobacteria may contribute to both the serrated pathway and the adenoma-carcinoma sequence.