This research extended the theory of planned behaviour (TPB) with familiarity, trust, and perceived risk to examine the consumers' online purchase intention in Sri Lanka. Data were collected from 250 postgraduate students enrolled in eight universities and higher education institutes in Sri Lanka. Structural equation modelling confirmed the role of trust and familiarity as antecedents to customer intention. However, contrary to the expectations, perceived risk was not identified as a key determinant of customer intention. Further, among the three classical variables (attitude, subjective norm, and perceived behaviour control) of the TPB model, only attitude had a significant effect on customer intention. Amongst all the factors, trust was identified as the most influencing factor on customer intention. The extended TPB model could satisfactorily predict the customer intention with up to 46% variation of the customer intention.