In recent decades, integrated language competence has been highlighted in the language curricula taught in schools and institutions, and the relationship between test-takers' performance on integrated tasks and comprehension sources has been much studied. The current study employed the frameworks of reading and listening comprehension processes to examine the difference between the effects of reading competence and listening competence on integrated writing performance. A total of 152 Secondary 5 students from five local schools in Hong Kong responded to three tasks, including an independent listening task, an independent reading task and an integrated writing task. The reading cognitive skills contributed more towards the performance of the integrated writing task than the listening cognitive skills did. Furthermore, the interaction between the relationships of reading and listening to the integrated writing performance was significant. Three subskills each for both listening and reading that belong to higher-order thinking skills--"Elaborating, Evaluating" and "Creating"--had significant correlation with integrated writing performance. Implications for the teaching of integrated writing were also discussed.