This paper discusses uniquely fractional colourable graphs. Suppose r=n/k is a rational. Two definitions of uniquely r-fractional colourable graphs are given, and we prove that the definitions are equivalent. Then we prove that for any rational n/K≥2, for any integer g, there exists a uniquely n/k -fractional colourable graph G of girth at least g, and of maximum degree at most 5n13k.