By using urea as the new nitrogen source, for the first time, Sc-based metal nitride clusterfullerenes (NCFs), Sc3N@C2n (2n=80, 78, 70, 68), have been synthesized successfully. The optimum molar ratio of Sc2O3/CO(NH2)2/C for the synthesis of Sc NCFs is 1:3:15. The yield of Sc3N@C80 (Ih+D5h) per gram of Sc2O3, using CO(NH2)2 as the new nitrogen source, was quantitatively compared to those obtained when using the reported nitrogen sources, including N2, NH3, and guanidinium thiocyanate. We find that there is a clear difference on the selectivity of Sc-based NCFs within the extract mixture obtained from one rod and accumulative two rods. According to discharging experiments and XRD analysis, we conclude that NH3 generated in situ from the decomposition of CO(NH2)2 is mainly responsible for the formation of Sc-based NCFs when using only one rod, whereas in the second rod CO(NH2)2 would decompose into melamine during discharging of the first rod. Thus, the selectivity of fullerenes is clearly dependent on the decomposed product of CO(NH2)2. Finally the difference in the decomposition behavior of CO(NH2)2 and melamine was studied in detail and a possible decomposition process of CO(NH2)2 during discharging was proposed. Accordingly, the difference in the selectivity and yield of Sc NCFs for CO(NH2)2 and melamine was interpreted.