This paper presents a finite-element model of the Phu My Bridge, a 380m-main span reinforced concrete cable-stayed bridge in Ho Chi Minh City, Vietnam. The model is also updated based on accelerometer data from the on-structure sensing system for structural health monitoring (SHM). A comprehensive sensitivity study is undertaken to examine the effects of various structural parameters on the modal properties, according to which a set of structural parameters are then selected for model updating. The finite-element model is updated in an iterative procedure to minimise the differences between the analytical and measured natural frequencies. The model updating process converges after a small number of four iterations, due to the accuracy of the initial model which was achieved through careful consideration of the structural parameter values for the model, optimal element discretisation for mesh convergence, and the most sensitive parameters for updating. The updated finite-element model for the Phu My Bridge is able to reproduce natural frequencies in good agreement with measured ones and can be helpful for long-term monitoring efforts.