Functional languages and logic languages complement each other in the following sense. Functional programming languages, based on reduction, have properties such as deterministic evaluation and lazy evaluation; however they lack some desirable properties such as existentially quantified variables and partial data structures. On the contrary, logic programming languages, based on Horn clause logic and resolution, allow existentially quantified variables and partial data structures but lack both deterministic evaluation and lazy evaluation. From this point of view it is natural to inegrate functional and logic programming languages into one paradigm.This provides a unified language with more expressive power than both logic and functional languages.This pa-per discusses the proposal for an operational semantics of functional logic languages,and demonstrates tthat the operational semantics is practically visible.