Thulium-Doped Fiber Amplifier (TDFA) are considered for long-haul transmission systems as they allow amplification in the S-band (1.46- 1.53 μm) thanks to the Tm3+ emission at 1.47 μm from the 3H4-3F4 transition. Presently TDFA are fluoride based because of the low phonon energy of this glass. But as it presents some drawbacks (reliability, splice to silica, ...), we propose to realize a silica-based TDFA. The fibre under investigation in this article has a high A12O3 concentration in order to improve the efficiency of the 1.47 μm-thulium emission. The fiber has a low Tm concentration, around 40 ppm mol, a 16.5×10-3 refractive index and a core radius of 2.3 μm. Lifetime from the 3H4 and 3F4 levels were measured to be 58 μs and 540 μs, respectively. Gain measurements were conducted using a single wavelength pumping scheme at 1060 nm and 1 W of pump power. Although the highest measured gain was 0.9 dB for a 4m long fiber, this experimental result was compared with numerical modeling. From these simulations, we estimate the characteristics of the fibre to increase the gain up to 20 dB.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.