The purpose of this study is toclassify defining sentences in science textbooks and analyse them onthe basis of their lexico-grammatical patterns as well as their rolesin the text. Many studies have focused on the concepts of ‘definingstrategy’ or ‘defining sentence types’ in lexicography. In addition, theuse of defining strategies appears to be more important in scienceprose, when describing scientific terms, than in any other fields.While previous studies have examined definition in Koreandictionaries, only a few have looked into what grammaticalcharacteristics the science textbooks present in terms of definingstrategy and what role these various patterns play in definingscientific terms. This study is organized as follows. Chapter 2 dealswith issues relating to the analysis of the defining sentences andpresents the methodology and corpus construction. Chapter 3classifies the Korean defining sentences by analysing the definitionpatterns of Korean dictionaries. Chapter 4 analyzes manually 200defining sentences in Korean science textbooks and classifies themaccording to not only their lexico-grammatical patterns but also theirfunctions