A highly sensitive temperature sensor was made by use of a side-hole glass fiber filled with indium metal, and its optical properties were investigated. The temperature sensitivity of the fiber-optic temperature sensor was $d\lambda /dT=-7.38\mathrm{nm}/\mathrm{K}$. The temperature sensitivity was also examined in sensors made by different lengths of the side-hole fiber and the indium-filled fiber region. The temperature sensitivity could be varied in the range of $-1.83$ to $-7.38\mathrm{nm}/\mathrm{K}$ by changing the relative length between the side-hole fiber and the indium-filled fiber region.