The purpose of this study is to describe the existence of Bi’ah lughawiyah in increasing students' mufrodat in Nurul Islam women’s dormitory Tengaran Boarding House. This research is descriptive qualitative. Techniques of data collection using observation, tests, interviews and documentation. Data analysis techniques according to Matthew B. Miles and A. Michel Huberman (data collection, Data Reduction, Data Presentation, Conclusion). The results showed that the activities that took place at Bi’ah lughawiyah were Language Tutorials, Speeches (Muhadarah), Muhadasah, Language Time, Drilling, Mahrojan Lughawi. The existence of Bi’ah lughawiyah as a forum to improve students' mastery of mufrodat in practicing Arabic as a language of everyday instruction in communication in the environment of the Nurul Islam Tengaran women's dormitory. Although basically not all students' mastery ability is influenced by the existence of Bi'ah lughawiyah. There are other factors that also influence students' mastery of mastery skills obtained from previous educational backgrounds, namely alumni from Islamic-based elementary schools with mean = .75, standard deviation = 5.82, and standard error = 0.77.