In Electronic Convenient Store, customers needautomatic purchase-sale system that is workable anytimeand anyplace. This paper proposes WAP-based automaticpurchase-sale system for Convenient Store’s ECommerceto help Small and Medium Enterprises(SMEs) in local competitive sale and energy saving byordering goods via client’s mobile phone. This systemcomprises of client, WAP gateway and server units. Themodification of PHP, Visual Basic and Mysql databasewhich used world wide for Internet system, WML inwireless protocol are employed to create client-WAPgateway and WAP gateway-server interfaces. Stockcontrol, product sale and bill processing units withmultimedia are provided at the server side in order toautomatically handle purchase and sale whenever andwherever the customers access. To evaluate theperformance of proposed system, we performedsimulation and experiments by on-line viawww.utccmart.com domain. The results reveal theproposed system is workable and mean satisfactory fromsample customers.