Objective To investigate the occurrence of unplanned readmission in the elderly patients with comorbidities and to explore the effect of geriatric syndrome on unplanned readmission. Methods From January 2015 to December 2017, a total of 443 elderly cases with comorbidities were selected, who were hospitalized in Department of Geriatrics of the Fifth People′s Hospital of Chengdu. Geriatric syndrome was screened by comprehensive geriatric assessment, the patients were followed up for two years after discharge, and data were collected of the unplanned readmission within the period. Statistical analysis was performed using SPSS statistics 24.0, and independent risk factors were screened out by multivariate logistic regression analysis. Results Within the two-year follow-up, 199 (44.92%) patients were readmitted without plan. The top 5 in the geriatric syndrome were the dependence for activity of daily living (ADL) (n=269,60.72%), risk of malnutrition (n=256,57.79%), high-risk of fall (n=246,55.53%), multiple medications (n=237,53.50%), and weakness (n=231,52.14%). Multivariate logistic regression found that malnutrition (OR=1.522, 95%CI 1.081-2.145; P=0.016), high-risk of fall (OR=1.855,95%CI 1.219-2.825; P=0.004), ADL impairment (OR =1.649,95%CI 1.074-2.533; P=0.022), polypharmacy (OR=1.597,95%CI 1.068-2.388; P=0.023) were independent risk factors for readmission within 2 years. Conclusion The readmission rate in elderly patients with comorbidities is high, and the geriatric syndrome has effect on the time and frequency of readmission.