Objective To investigate the combined effects of chronic obstructive pulmonary disease (COPD) and depression on spatial memory in old rats, aiming to better understand the comorbidity of the two diseases in geriatric patients. Methods The SD rats were assigned into five groups: adult control group (n=6), elderly control group (n=6), elderly COPD group (n=6), elderly depression group (n=6) and elderly COPD with depression group (n=6). Smoking and chronic unpredictable mild stress (CUMS) with solitary support were used to induce COPD model, depression model, respectively, and the both were applied for the comorbidity model. Learning and memory deficits were assessed by Morris water maze (MWM) test. The activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in serum and hippocampus tissue were determined by Xanthinoxidase method and Thiobarbituric acid reaction (TBAR) method, respectively. Results The results of pulmonary histology, lung function, open-field test and sucrose consumption demonstrated the comorbidity models of COPD and depression in elderly rats were successfully established using smoking and CUMS with solitary support. Compared with the elderly control group, the group of COPD with depression had obviously longer time of latency and longer travel distance to reach the platform in MWM test (LSD-t=-10.116, P=0.000; LSD-t=-6.448, P=0.000). The SOD activity in serum and hippocampus decreased significantly (LSD-t=2.629, P=0.014; LSD-t=2.215, P=0.044) and the MDA content in serum and hippocampus increased significantly (LSD-t=-2.140, P=0.042; LSD-t=-2.070, P=0.049) in elderly COPD with depression group. Conclusions COPD in comorbidity of depression could induce spatial memory deficit in old rats. The mechanisms might be related to the overloaded and free radical metabolic imbalance. These results suggest a potential therapeutic target for comorbidity of COPD and depression in geriatric patients.