The Arden Syntax is a language for expressing computable medical decisions. It was developed and published under the direction of Health Level Seven, Inc (HL7), and is a standard of the American National Standards Institute (ANSI). It is used to construct executable Medical Logic Modules (MLMs) that represent individual clinical decisions. The authors introduced brief explanation of the Arden Syntaxand gave an example to help readers understand it with easy. Although Arden Syntax is the HL7 standard, there are problems related to the adoption of Arden Syntax as the standard tool for describing medical logic: the curly-braces problem, and the compiler problem. GELLO as well as virtual Medical Record based on the HL7 Reference Information Model (RIM) may provide solutions to the former problem. The latter problem would be resolved by introducing XML based expression of Arden Syntax, the ArdenML: the next generation of Arden Syntax. Unfortunately, Korean hospital information systems are not yet ready to adopt clinical decision support system including Arden Syntax. However, when Arden Syntax version 3.0 (ArdenML) with Korean rule-base engines is introduced into the hospital information system, it would be easier to build up clinical decision support system in Korea.