In this paper, the effect of deposition rates and annealing on the optical properties of vacuum deposited pentacene (C22H14) thin films on glass substrates are reported. Thin films of pentacene were deposited on glass substrates using resistive evaporation technique. Optical properties of the pentacene thin films deposited for different deposition rates of 5Å/s, 10 Å/s and 20Å/s were studied. Results revealed that the optical band gap was more for the device with active material deposited at a lower deposition rate of 5 Å/s. Optical properties of the vacuum annealed (100 °C, 150 °C and 200 °C) pentacene thin films were also done and it was found that optical band gap slightly increased for the films annealed at a temperature of 100 °C and after that it remains same for the samples annealed at higher temperatures. This small optical band gap makes this material suitable for photovoltaic applications.