Purpose -The purpose of this paper is to determine the factors that influence the intention to use and actual usage of a G2B system such as electronic procurement system (EPS) by various ministries in the Government of Malaysia. Design/methodology/approach -The research uses an extension of DeLone and McLean's model of IS success by including trust, facilitating conditions, and web design quality. The model is tested using an empirical approach. A questionnaire was designed and responses from 358 users from various ministries were collected and analyzed using structural equation modeling (SEM). Findings -The findings of the study indicate that: perceived usefulness, perceived ease of use, assurance of service by service providers, responsiveness of service providers, facilitating conditions, web design (service quality) are strongly linked to intention to use EPS; and intention to use is strongly linked to actual usage behavior. Practical implications -Typically, governments of developing countries spend millions of dollars to implement e-government systems. The investments can be considered useful only if the usage rate is high. The study can help ICT decision makers in government to recognize the critical factors that are responsible for the success of a G2B system like EPS. Originality/value -The model used in the study is one of the few models designed to determine factors influencing intention to use and actual usage behavior in a G2B system in a fast-developing country like Malaysia.