Background: Researchers have integrated cross-cultural communication (CCC) with writing to examine students’ writing performance, motivation, and perceptions in EFL classrooms. However, the exploration of how authentic CCC with students from different cultural backgrounds benefits lower-proficiency students’ English writing competence and motivation remains underexplored. Purpose: This mixed-methods study, employing pre-test and post-test designs, examined the effects of asynchronous CCC on EFL university lower-proficiency students’ writing performance, motivation, and perceptions to determine whether asynchronous CCC facilitated EFL lower-proficiency students’ writing competence and motivation and to elucidate its impact on their writing performance. Method: Twenty-nine freshmen, who were non-English majors, were divided into lower-proficiency (N=15) and higher-proficiency (N=14) groups. Data were collected from the writing tests and Writing Motivation Questionnaires (WMQ) completed in the pre-test and post-test. The questions in the writing tests were identical in both tests, while the WMQ comprised 33 five-point Likert-scale questions and an open-ended question aimed at exploring the students’ motivation and perceptions regarding writing in this study. Results: The results indicate that the features of social interaction and cross-cultural engagement within asynchronous CCC significantly developed lower-proficiency students’ writing performance and mitigated their negative writing motivation. Utilising asynchronous CCC, which facilitated feedback exchange and collaborative writing with higher-proficiency peers, notably bolstered lower-proficiency students’ writing proficiency. Additionally, the integration of meaningful, intriguing, and authentic asynchronous CCC activities contributed to reducing negative writing motivations among lower-proficiency students. However, delayed responses from online peers and a sense of demotivation while collaborating with lower-proficiency peers may have contributed to the insignificant development observed among higher-proficiency students. Conclusion: Engaging EFL university lower-proficiency students in asynchronous CCC to exchange cultural and linguistic knowledge could enhance their writing performance and reduce their negative writing motivation. This is because the features inherent in asynchronous CCC render English writing meaningful, intriguing, and authentic.