In this paper, we fabricate a very low-loss single-mode polymer optical waveguide at 1550-nm wavelength. For the single-mode waveguide fabrication, we apply a silicate based organic-inorganic hybrid resin, SUNCONNECT developed at Nissan Chemical Ind. Ltd. In the SUNCONNECT resin, the concentration of carbon-hydrogen bonding is lower than those in other conventional organic polymers, so the absorption loss at near infra-red region inherent to the carbon-hydrogen bonding is reduced: the propagation loss of the fabricated single-mode waveguide is as low as 0.5 dB/cm at 1550 nm, which is remarkably lower than the loss (approximately 1 dB/cm in general) of conventional organic polymer based waveguides at the same wavelength. The unique feature of this paper is in the fabrication method: the Mosquito method is applied. We succeeded in reducing the core diameter to less than 10 μm, and even a 3-μm core diameter is achieved. In the Mosquito method, the core is formed by horizontally scanning a needle with dispensing a core monomer into a cladding monomer. Here, the tip of the needle remains inserted into the cladding monomer while scanning.