In recent years, it has become clear that, in addition to normal cytokines, phospholipid mediators play an important role in the development, growth, infiltration, and metastasis of cancer and in the cancer microenvironment. A phospholipid analysis method using tandem mass spectrometry (LC-MS/MS) with high detection sensitivity has enabled quantification of phospholipids, even when using a very small sample. To date, we had applied this MS technology to colorectal cancer tissue. Therefore, in this study, this mass spectrometry technique was applied to ulcerative colitis (UC) and UC-related colorectal cancer, and an analysis was conducted with the aim of clarifying which lysophospholipids specifically change in each type of tissue. UC-associated colorectal cancer tissue and UC mucosa were collected from surgical specimens of colitic cancer (n=3). Cancerous and non-cancerous tissues were collected from surgical specimens from patients with sporadic colorectal cancer (n=11). After extraction from these tissues, the amounts of lysophospholipids were quantified by LC-MS/MS. In addition, lysophosphatidylserine (LPS) and lysophosphatidylinositol (LPI) were quantified for each molecular species of fatty acids. Compared to normal mucosa, LPI was increased 3.8-fold (p<0.001) and LPS 3.5-fold (p<0.001) in UC-related colorectal cancer. Molecular species of LPI which were increased in UC-related colorectal cancer were 18:0 (p=0.001), 16:0 (p=0.03) and 20:4 (p=0.004), and of LPS were 18:0 (p<0.001) and 22:6 (p=0.014). Lysophospholipids increased in colorectal cancer and in UC-associated colorectal cancer. In particular, LPI may have contributed significantly to colitis-associated carcinogenesis.