Objectives To identify factors associated with length of stay (LOS) in chronic obstructive pulmonary disease (COPD) hospitalised patients, which may help shorten LOS and reduce economic burden accrued over hospital stay. Design A retrospective cohort study. Setting This study was performed in a tertiary hospital in China. Participants Patients with COPD who were aged >= 40 years and newly admitted between 2016 and 2017. Primary and secondary outcome measures LOS at initial admission was the primary outcome and health expenditures were the secondary outcome. To identify factors associated with LOS, we collected information at index hospitalisation and constructed a conceptual model using directed acyclic graph. Potential factors were classified into five groups: demographic information, disease severity, comorbidities, hospital admission and environmental factors. Negative binomial regression model was fitted for each block of factors and a parsimonious analysis was performed. Results In total, we analysed 565 patients with COPD. The mean age was 69 +/- 11 years old and 69.4% were men. The median LOS was 10 (interquartile range 8-14) days. LOS was significantly longer in patients with venous thromboembolism (VTE) (16 vs 10 days, p=0.0002) or with osteoporosis (15 vs 10 days, p=0.0228). VTE ((rate ratio) RR 1.38, 95% CI 1.07 to 1.76), hypoxic-hypercarbic encephalopathy (RR 1.53, 95% CI 1.06 to 2.20), respiratory infection (RR 1.12, 95% CI 1.01 to 1.24), osteoporosis (RR 1.45, 95% CI 1.07 to 1.96) and emergence admission (RR 1.08, 95% CI 1.01 to 1.16) were associated with longer LOS. In parsimonious analysis, all these factors remained significant except emergency admission, highlighting the important role of concomitant morbidities in patients' hospital stay. Total hospitalisation cost and patients' out-of-pocket cost increased monotonically with LOS (both p(trend) <0.0001). Conclusion Patients' concomitant morbidities predicted excessive LOS in patients with COPD. Healthcare cost increased over the LOS. Quality improvement initiatives may need to identify patients at high risk for lengthy stay and implement early interventions to reduce COPD economic burden.