Objective To investigate the population composition and seasonality of rodents and their density in different habitats in Liaoning province, China, and to provide a scientific reference for developing rodent control strategies. Methods Two types of monitoring points were chosen in cities (and towns), one type in residential area and the other in special industrial area. Additionally, two types of monitoring points were chosen in rural areas, one type in villages and the other out of villages. The density of rodents was monitored by night trapping. Results Totally 506 806 traps were set up in Liaoning province from 2009 to 2013. There were 485 792 effective traps, which captured 7548 rodents. The average density of rodents was estimated to be 1.55%, with a higher level in villages (2.25%) than in cities (0.93%). The density of rodents was highest in natural villages (2.25%), followed by special industrial areas (1.09%) and residential areas (0.78%) in cities. Seasonal fluctuations of rodent density in total, individual years, or different habitats followed a double-peak curve. Two peaks of rodent density occurred in April to May and in September to October, respectively. Rattus norvegicus was the dominant species of rodents in Liaoning province. Conclusion The density of commensal rodents in Liaoning province showed a slightly increasing trend from 2009 to 2013. Seasonality of rodent density followed a double-peak curve. The control of rodent density should focus on rural areas. According to their characteristics of seasonal fluctuations, comprehensive preventive measures should be taken to reduce the density of rodents in the two peak periods, in order to control rodent-borne diseases.