This study explored the effects of outlining on the summaries of thirty six L2 college students across three text genres and their opinions on the use of outlining in writing the summaries. Over the eight weeks, the students were divided into an outlining group (experimental group) and a keyword group (controlled group) wrote three summaries after reading articles across three genres (e.g. argumentative, expository, and narrative) at two weeks intervals. Additionally, a follow-up questionnaire on the use of outlining in writing summaries was conducted. Data were analyzed by the Syntactic Complexity Analyzer (Lu, 2010) under 14 indices, and the responses to the questionnaire were analyzed by percentages. The results found a statistically significant difference appearing only in the aspect of CT (i.e. clause per T-unit). In addition, a majority of students utilizing outlining for summary writing believed that they were helped not only to understand the contents and the structure of the articles, but to write summaries with their own words. These results have a pedagogical meaning in that outlining can be more efficient for specific reading genres when teaching summarization in L2 classes.