The fluorescent characteristic in Nd: YAG single crystal fibers has been investigated. One rod and four claded fibers produced with MPG process were tested, of which the diameters ranged from 41 micron to 120 micron with variations less than 0.5%. Excited by 300 milliwatt power laser at 0.6 micron, the fluorescence amplification at 1.06 micron was observed. The analysis predicted the condition and capability of superfluorescence.