A study was conducted at the citrus nursery of the National Horticultural Research Institute(NIHORT) Headquarters, Ibadan to investigate the effect of different rate and frequency of Nitrogen(N) fertilizer applications on the growth of Cleopatra mandarin (Citrus reticulata Blanco) rootstock seedlings. Four rates of N fertilizer 0,200,300 and 400kg/ha were applied at three different doses: single, two splits and three splits on six-month old Cleopatra mandarin rootstock seedlings. It was a factoral layout in randomized complete block design. Results indicated that fertilized plots gave significantly higher plant height, number of leaves, stem girth and leaf area when compared to control (no fertilization). There were no significant differences in the growth attributes between fertilized plots. Frequency of fertilizer application had no influence on Cleopatra mandarin rootstock seedlings. Considering economic implications, 200kgN/ha was better and it is therefore recommended for Cleopatra mandarin rootstock seedlings in the nursery.