We report the experimental observation of dispersion transition from abnormal dispersion (fast light) to normal dispersion (slow light) in a side-coupled ring resonator. We reveal that the transition from fast light to slow light can occur, when the tuned loss of the resonator results in the experience from the undercoupled regime to the overcoupled regime. Also, we experimentally fabricate the fiber side-coupled ring resonator, and measure the group delay of the resonator by coupling the resonator to a fiber Mach-Zehnder interferometer (MZI). The measured experimental results demonstrate the dispersion transition, and are in good agreement with the corresponding theoretical results. The sidecoupled resonator with the tunable dispersion (group delay) can exploited for optical storage devices, slow light Fourier transform (FT) interferometric spectrometers, white light cavities (WLCs), optical switches, optical routers, and optical sensors.