The transmission line is a vital part of an electric power network. Precise knowledge about the parameters of a transmission line is important to perform power system operation, control and, to design a line protection system. This paper puts forward a method to estimate parameters of a transmission line based on a short transmission line model and the line input-output data such as voltage, current, power and/or power factor at each end of the line. The firefly algorithm, a swarm intelligence optimization technique, is used to estimate parameters of the line model by defining an error minimization objective function. It is concluded that the presented approach is significant in estimating the line parameters with high accuracy. The estimated parameters are in precision with the actual line parameters indicated by the low relative error.