Polymerization of 1-(trimethylgermyl)-1-propyne (TMGP) with TaCl5 and NbCl5 produced a colorless polymer in high yields, whose molecular weight reached about 3 x 10(5)-14 x 10(5). The molecular weight distribution of the poly(TMGP) with NbCl5 in cyclohexane was somewhat narrow (M-w/M-n = similar to 1.54). The TaCl5-based poly(TMGP) dissolved in toluene, chloroform, cyclohexane, carbon disulfide, carbon tetrachloride, tetrahydrofuran, hexane, and so forth; the NbCl5-based polymer was less soluble and did not dissolve in hexane, despite its lower molecular weight;. The cis contents of the NbCl5- and TaCl5-based poly(TMGP)s determined by C-13 NMR were 67 +/- 5 and 28 +/- 3%, respectively. The onset temperature of the weight loss of poly(TMGP) in air was 350 degrees C, indicating fair thermal stability. The oxygen permeability coefficient (P-O2) of poly(TMGP) at 25 degrees C was 7800 barrer after the methanol conditioning, and the permeability was fairly stable to aging.