A processable polyborazine precursor was synthesized via substitution reaction and deamine condensation reaction by using methylamine, propylamine and B-trichloroborazine (TCB) as the starting materials. The chemical composition, structure and properties of the obtained polymer were investigated using element analysis, FT-IR, NMR, XPS and TG. The results indicated that the backbone of the polymer was approximate linear arrangement of boron-nitride ring molecules with B-N(CH3)-B structure as bridge bond, meanwhile minor amount of methylamino and propylamino remained in polyborazine as the pendant or end group. The melting point, number average molecular weight and polydispersity index of polyborazine was 90°С , 1002 and 1.355, respectively. The polyborazine showed good processability and polyborazine precursor fibers with diameter of 10~15 µm could be obtained by melt-spinning in N2 atmosphere. The ceramic yield of the polyborazine at 1000°С in nitrogen atmosphere was 53.2 wt%, which suggested that the as-achieved polymer can be used as a precursor to boron nitride ceramic fibers and membranes.