In this study, we investigated the characteristics of lesson planning of pre-service secondary science teachers and the factors which influenced in their lesson planning. Thirteen pre-service secondary science teachers at a college of education in Seoul participated in this study. Teaching-learning materials such as lesson plans and handouts, and lesson planning journals written by the pre-service teachers were collected. Semi-structured interviews were also conducted to obtain information about their lesson planning activities. The analyses of the results revealed that most of the pre-service teachers did not systematically consider the national science curriculum and focused on planning one lesson only. Instructional objectives were not only considered as minor element in lesson planning, but also limited to cognitive domain. Devising teaching-learning strategies was found to be the starting point of the lesson planning. They accommodated constructivistic teaching-learning theory presented in their method courses through reflective evaluation of the experiences of learning in their secondary schools. The experiment activities that were presented in the textbooks were used themselves when they planned experiments as student activities, but other activities were planned depending on their personal experiences. Most pre-service teachers did not plan assessment because they could not recognize it as an element of lesson planning. These results may offer some implications in educating pre-service secondary science teachers on lesson planning.