The TDFA (Thulium-Doped Fiber Amplifier) is a promising candidate for an amplifying device in S band. We established a bi-directionally pumped Thulium-Doped Silica Fiber Amplifier (TDSFA) with a single 1 064 nm pump wavelength in order to know the characteristics of the amplifier. The on-off gain was measured for simplicity. The gain varying with pump power and with signal wavelength was studied in detail. At the maximum launched pump power of 1 400 mW, the amplifier had a gain over a wide wavelength region of 1 485 to 1 517 nm, with a peak gain of 3.76 dB. Weak GSA (Ground-State Absorption) and strong ESA (Excited-State Absorption) limit the further increase of the gain. The results show that TDSFA is operable using such an upconversion pumping scheme.