Abstract: The aim of this study was to investigate the effects of nitrogen (N) fertilizer on the activity of N metabolism and growth of two maize (Zea mays) cultivars with contrasting tolerance to low N. An experiment was laid out in a split-plot design with three replicates. The main plot consisted of two maize cultivars with contrasting tolerance to low N (the low-N tolerant cultivar ZH311 and the low-N sensitive cultivar XY508). The split plot consisted of six N treatments: 0, 90, 180, 270, 360, and 450 kg/ha. The chlorophyll content and the activities of enzymes involved in N metabolism (NR: nitrate reductase, GS: glutamine synthetase, GDH: glutamate dehydrogenase) at late growth stages were determined, as well as the seed protein content and yield. The results showed that N fertilizer increased chlorophyll content and enzyme activities at late stages, and promoted protein content and yield. As the amount of N fertilizer increased, these indexes increased to a greater extent in XY508 than in ZH311, while all indexes were higher in ZH311 than in YX508. Compared with the low-N sensitive cultivar, the low-N tolerant cultivar retained a higher chlorophyll content and higher activities of enzymes involved in N metabolism, especially at the mid to late grain-filling stage. In addition, the low-N tolerant cultivar required low to mid N levels to improve seed protein content and yield. These results provide information about the physiological mechanisms involved in tolerance to low-N conditions.