Increasing of traffic intensity due to technology advancement in heavy axle vehicles affects overall integrity of highway bridges. Along with the traffic intensity, aging of structural elements leads to distress of structure. Due to distressing in structural elements, stiffness gets reduced. Research studies based on vibration test methodology shows that change in fundamental frequency of any structures is directly related to overall stiffness of the structure. Therefore, many research studies have been carried out across the globe by researchers in the field of vibration based monitoring of the structure to identify dynamic behaviour by using properties such as natural frequencies, mode shapes and modal damping ratios. In this paper, ambient vibration test on a bridge where measurements taken with instrumentation of acceleration sensors on the bridge span. For the study, concrete I girder bridge on the ring road over Sabarmati River near Ahmedabad City is selected. The bridge is characterized by a system of post-tensioned I girder simply supported beams with span. The dynamic characteristics of the bridge were computed by using Stochastic subspace identification (SSI) method and Least squares complex frequency domain (LSCF) Method, which is further used to study fundamental frequency of bridge.