Objective To investigate the correlation between monocyte-lymphocyte ratio (MLR) and intensive care unit (ICU) results in ICU hospitalized patients. Methods Clinical data were extracted from Medical Information Mart for Intensive Care Ⅲ database, which contained health data of more than 50000 patients. The main result was 30-day mortality, and the secondary result was 90-day mortality. The Cox proportional hazards model was used to reveal the association between MLR and ICU results. Multivariable analyses were used to control for confounders. Results A total of 7295 ICU patients were included. For the 30-day mortality, the hazard ratio (HR) and 95% confidence interval (CI) of the second (0.23≤MLR<0.47) and the third (MLR≥0.47) groups were 1.28 (1.01, 1.61) and 2.70 (2.20, 3.31), respectively, compared to the first group (MLR<0.23). The HR and 95%CI of the third group were still significant after being adjusted by the two different models [2.26 (1.84, 2.77), adjusted by model 1; 2.05 (1.67, 2.52), adjusted by model 2]. A similar trend was observed in the 90-day mortality. Patients with a history of coronary and stroke of the third group had a significant higher 30-day mortality risk [HR and 95%CI were 3.28 (1.99, 5.40) and 3.20 (1.56, 6.56), respectively]. Conclusion MLR is a promising clinical biomarker, which has certain predictive value for the 30-day and 90-day mortality of patients in ICU.