Praseodymium-doped glasses were prepared in the Ga-Na-S (GNS) system and their optical properties were studied. A single-mode fiber with an attenuation loss of 1.2 dB/m at a wavelength of 1.31 mu m was fabricated using an extrusion method, and the amplification characteristics were measured in the bidirectional pumping configuration. We demonstrated a gain coefficient of 0.81 dB/mW at a wavelength of 1.34 mu m, which is the highest we have ever reported, and achieved a net gain of 32 dB for a pump power of 90 mW, Highly efficient optical amplification at a wavelength of 1.3 mu m was demonstrated in the praseodymium-doped GNS fiber.