This study aims to investigate to what extent pre-task planning and the source text type(genre) affect Korean English as a Foreign Language (EFL) college learners' summary writings in terms of lexical, sentential, and discourse-level features. A total of 120 summary writings of cause/effect expository texts and argumentative texts in the different modes of planning were collected and analyzed using a computational assessment tool, Coh-Metrix. The results show that the participants' summary writings in the different planning conditions and text types were statistically different according to their lexical-level (the mean word length, word frequency, imageability, concreteness, the third person pronouns), sentential-level (the mean sentence length, causal connectives, temporal connectives, noun density, Flesch-Reading Ease (FRE), Flesch-Kincaid Grade Level (FKGL)), and discourse-level (type-token ratio, LSA cosines for all and adjacent sentences) features. This study provides some pedagogical implications for teaching English summary writings of various planning contexts and source text types.