Abstract： Objective:To analyze the correlation between lactate dehydrogenase (LDH) and the risk of brain metastases in small cell lung cancer (SCLC).Methods:A total of 86 SCLC patients treated in our hospital from October 2018 to October 2021 were selected and followed up until September 30, 2023. MRI results showed that 25 patients with brain metastasis were in the observation group and 61 patients without metastasis were in the control group. General data, laboratory indicators and LDH levels of the two groups were collected, and factors related to SCLC brain metastases were analyzed by multivariate Logistic regression.Results:There were 16 survivors(64.00%), 9 deaths (36.00%) in the observation group and 58 survivors(95.08%), 3 deaths (4.92%) in the control group. In the observation group, there were 16 cases (64.00%) of smoking history, 4 cases (16.00%) of tumor node metastasis (TNM) stage ⅠA, 8 cases (32.00%) of ⅡB and 13 cases (52.00%) of ⅢA. In the control group, there were 23 cases (37.70%) of smoking history, 27 cases (44.26%) of TNM stage ⅠA, 28 cases (45.00%) of ⅡB stage and 6 cases (9.84%) of ⅢA stage. The comparison between the two groups was(P<0.05). In the observation group, neuron-specific enolase (NSE) (41.63±12.75) ng/ml, carcinoembryonic antigen(CEA) (21.93±6.25) ng/ml, LDH[(253.62±74.36)U/L, hemoglobin (82.54±5.65)U/L; In the control group, NSE (32.52±10.58)ng/ml, CEA (16.54±4.82)ng/ml, LDH (182.42±56.98)U/L, Hb (91.37±6.12)g/L, and P<0.05. Multivariate Logistic regression analysis showed that TNM stage (OR=2.712, 95%CI: 1.186-6.201), NSE (OR=1.073, 95%CI: 1.014-1.136), CEA (OR=1.216, 95%CI: 1.085-1.363), LDH(OR=1.026, 95%CI: 1.015-1.038) were risk factors for BMS, Hb (OR=0.770, 95%CI: 0.685-0.865) were protective factors for BMS.Conclusion:SCLC has a higher risk of brain metastases. Serum LDH is an influential factor of brain metastases and is positively correlated with the risk of brain metastases.