Objective:To explore the correlation between blood homocysteine(Hcy) level and cognitive function in elderly patients with frailty syndrome.Methods:Sixty elderly patients with frail syndrome who were hospitalized in Ningbo Mental Hospital from September 2022 to June 2023 were selected retrospectively, they were divided into the cognitive normal group (24 cases) and the cognitive impairment group (36 cases) based on the presence of cognitive impairment. The Matrics Consensus Cognitive Battery (MCCB) score and serum Hcy levels of the two groups were compared, and the correlation between Hcy level and cognitive function were analyzed by Pearson test.Results:The MCCB scores in the cognitive impairment group were lower than those in the cognitive normal group, there were statistical differences ( P<0.05). The levels of serum Hcy, tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 in the cognitive impairment group were higher than those in the cognitive normal group: (17.89 ± 0.90) μmol/L vs. (16.99 ± 0.75) μmol/L, (33.39 ± 4.01) ng/L vs. (27.19 ± 4.81) ng/L, (23.67 ± 4.36) ng/L vs. (20.27 ± 4.23) ng/L, there were statistical differences ( P<0.05). Pearson test results showed that serum Hcy level were negatively correlated with alignment, symbol coding, word memory and learning, working memory/spatial span, reasoning and problem solving, visual memory and learning, social cognition and attention/alertness scores of MCCB ( r = - 0.292, - 0.443, - 0.475, - 0.418, - 0.370, - 0.391, - 0.324, - 0.367, P<0.05). Serum Hcy level was positively correlated with TNF-α and IL-6 levels ( r = 0.336, 0.326, P<0.05). Conclusions:There is a certain correlation between serum Hcy level and cognitive impairment in elderly patients with frail syndrome. When blood Hcy level increase, the symptoms of cognitive impairment in patients become more severe.