A method for managing a service bandwidth by a customer port and an EPON system using the same are provided. In order to manage the service bandwidth by a customer, ONU and ONT allocate a service class according to a combination of information about a customer that receives a service, and a service type and a service priority of a service provided to a customer, allocate a bandwidth according to each service class and control a uplink bandwidth or a downlink bandwidth according to a service class. Also, a system manger collects information about a service provider, a service provided from a service provider, a customer that receives a service, and information for classifying a service. After collecting, the system manager provides the collected information to the ONU and the OLT.