Dimethylhydrazine is a potential nitrogen precursor for organometallic vapor-phase epitaxy of GaN-based ternaries and quaternaries at relatively low temperatures. We have measured the vapor pressure of dimethylhydrazine and studied the pyrolysis characteristics of dimethylhydrazine in H-2 ambient. Results of co-pyrolysis with triethylgallium in H-2 ambient are also reported. The vapor pressure of dimethylhydrazine is given by Log P = 8.19-1780/T. Pyrolysis of the dimethylhydrazine is found to proceed by cleavage of the N-N bond followed by elimination of the methyl groups. Co-pyrolysis studies showed that an adduct and an intermediate dimer form at low temperatures then further decomposed at higher temperatures to the final product GaN.