A method and system using a processor for reasoning an optimized service of a ubiquitous system using context information and emotion awareness. The system using a processor for reasoning an optimized service of a ubiquitous system includes: a ubiquitous system unit to collect information about surroundings of a user; a context awareness unit to recognize a state of the user based on the information collected in the ubiquitous system unit, and to generate context information; an emotion awareness unit to recognize an emotion of the user based on the information collected in the ubiquitous system unit, and to generate emotion information; a combination unit to combine the context information and the emotion information; and a service selection unit to reason and select a service for the user based on the combination result of the combination unit.