This study investigated the impact of familiar versus unfamiliar environments on mobile-assisted language learning (MALL) task writing performance, English as a foreign language (EFL) writing proficiency, and learner perceptions. Fifty undergraduate students were divided into an experimental group and a control group. Both groups engaged in EFL learning in the classroom and later completed writing tasks in different learning environments outside the classroom: the experimental group in familiar environments and the control group in unfamiliar ones. Using a mobile learning system on tablet PCs, students completed five writing tasks describing resources in their environments, such as objects, people, situations, and scenarios. We assessed MALL task writing performance based on factors including the amount of writing, content quality, organization, creativity, grammar, and vocabulary, and compared results between the two groups. EFL writing proficiency was evaluated through a post-test directly related to the MALL tasks, and student perceptions of the MALL experience were measured through a survey. The results indicated that the experimental group outperformed the control group in both writing tasks and the post-test. Furthermore, the experimental group reported more positive perceptions of their MALL experience, reflected in higher emotional engagement and cognitive involvement. Based on these findings, we offer both theoretical insights into the role of familiar environments in facilitating language learning and practical suggestions for EFL teachers and researchers to incorporate real-world, contextually rich environments in MALL activities.