To investigate the relationship between oxysterols and mild cognitive impairment (MCI) in a matched case–control study. The plasma levels of four oxysterols, 27–hydroxycholesterol (27–OHC), 24S–hydroxycholesterol (24S–OHC), 7α–hydroxycholesterol (7α–OHC) and 7β–hydroxycholesterol (7β–OHC), were analyzed by High Performance Liquid Chromatography–Mass Spectrometry (HPLC–MS) and compared between 70 MCI patients and 140 matched controls with normal cognition. The odds ratio (OR) was calculated using logistic analyses to assess the association between oxysterols and MCI. Compared with controls with normal cognition, plasma level of 27–OHC was significantly higher in MCI patients. Logistic analyses suggested high plasma level of 27–OHC was significantly associated with MCI even after multivariate adjustment (OR = 2.86, 95 % CI: 1.52 ~ 5.37). Our findings suggested that the increased plasma level of 27-OHC was associated with MCI, suggesting high plasma levels of 27-OHC may pay an important role in the development of MCI.