We propose and demonstrate a tunable optical filter based on a tapered silica microcylinder, whose diameter is gradually varied along its longitudinal axis. The tapered microcylinder comprises a slowly varying transition zone fabricated through the fiber drawing technique. Given the tapered diameter of the microcylinder, the resonant wavelengths can be tuned by displacing the tapered microcylinder. This tunable filter exhibits a high Q-factor (～106) and a large tuning range (>1 free spectral range (FSR)).