A new ganglioside transformed strain isolated from soil was identified as Cellulosimicrobium sp. 21. It produced a sialidase which transformed polysialo-gangliosides GD1 and GT1 into a monosialoterahexosylganglioside, i.e., ganglioside GM1. The sialidase had both NeuAc-α-2,3- and NeuAc-α-2,8-sialidase activity without producing asiolo-GM1. The optimum conditions were evaluated and it was found that the transformation was optimally performed at 30 °C and pH 7.0. The substrate should be added at the beginning of the reaction and the concentration of substrate was 3% (w/v). Under these optimum conditions, Cellulosimicrobium sp. 21 converted GD1 and GT1 into GM1 in inorganic medium in a 5 L bioreactor with the recovery rate of 69.3%. The product contained 50.3% GM1 and was purified on silica to give the product with 95% of GM1 with a recovery rate of 30.5%. Therefore, Cellulosimicrobium sp. 21 has potential to be applied in the production of GM1 in the pharmaceutical industry.