The purpose of this study is to evaluate and analyze errors of business English letters composed by Korean secretaries. A total of eighteen business English letters of positive style were used for error evaluation conducted by eleven native English speakers in business. In the error analysis, major error types were identified as the following; the noun phrase errors, i.e., articles, misuse of possessives, the verb phrase errors, i.e., prepositions, auxiliary, and the adjective and adverb errors. Another types of critical errors were related to the inappropriate expressions and minor errors of mechanics. The error patterns of business English letters of Korean secretaries were identified by eleven English business specialists. This research also suggests the important guidelines for Korean secretaries to write concise and accurate English business letters for efficient business communication. It is recommended to choose appropriate and precise terms and expressions for business letter writing.