This paper employed the modified Theory of Planned Behaviour (TPB) model as a conceptual framework to assess the effects of three key beliefs of TPB: attitude, subjective norm and behavioural control, on e-government service acceptance and explain adopters' behavioural intention. Structural Equation Modelling (SEM) was applied to analyse a set of empirical data and the results show that attitude and behavioural control have significant effects on adopters' behavioural intention, which are consistent with past research both on IS product and e-commerce service. Although we found a significant indirect effect of subjective norm on intention from a competing model including interdependency terms between these three beliefs, the importance of subjective norm in the model needs further research to assess. This finding may partially make clear the important role of subjective norm in the modified TPB model in explaining the e-government acceptance behaviour.