Along with the increasing interest in integrated writing in L2 instruction, many studies have investigated language skills and cognitive processes involved in the task. However, relatively less is known regarding the roles of strategic and affective variables in predicting writing performance. The current study, therefore, investigates (a) how strategy, attitudinal, affective, and ability variables are related, and (b) how these variables predict performance in integrated writing. Predictor variables include proficiency, reading comprehension, vocabulary size, L2 strategy use, and attitudes toward reading and writing, and anxiety. Forty-three participants completed an L2 reading-writing integrated task, in which they read reading texts and wrote an essay summarizing the source text and arguing their opinions on the issue. Results showed that proficiency was positively related to reading-to-write strategies, and vocabulary size negatively to reading anxiety; however, ability-related variables generally had no or weak relationships with affective variables. Furthermore, only reading comprehension and reading anxiety were found to be significant predictors of performance in integrated writing.