Objective Rodent infestation monitoring is the foundation for rodent management in farmlands. The current study is to evaluate rodent population dynamics in the farmlands in Guangdong province, China, to compare the rodent density indices reflected by different methods, and to provide important baseline data for population management. Methods The rodent trace method and night trapping method were successively used to determine the rodent densities in the sampling areas. Rodent trace method: Two test lines were set along the irrigation channel or ridge, with a distance of more than 50 m in between; 50 mud stations (20 cm×20 cm) were set at a gap of 5 m on each test line. Night trapping method: Three hundred traps were set at night in each month; the distance between two traps was 5 m, and the distance between two test lines was more than 50 m; these traps were placed at night and collected in the morning of the next day. Results In the farmlands in Guangdong, the annual fluctuation in the density of rodent pests presented a bimodal pattern, and there were two peaks (in August and December) and two valleys (in September and February-March) every year. The capture rate, positive rate of rodent traces, and rodent trace index reflected the fluctuation in rodent population well and showed a significant linear positive correlation between each other; the linear regression equations were as follows: capture rate (Y)-positive rate of rodent traces (X): Y=0.115X＋1.119; capture rate (Y)-rodent trace index (X): Y=0.333X-1.078; positive rate of rodent traces (Y)-rodent trace index (X): Y=2.766X-16.332. Conclusion Night trapping method and rodent trace method have different advantages in the assessment of rodent populations in Guangdong farmlands and should be selected strategically according to specific circumstances.