This study determined the frequency and patterns of language alternation and the level of language proficiency among senior high school students in Wright I District, Schools Division of Samar. Utilizing a quantitative research approach with a descriptive research design, the study included fifty-seven (57) senior high school students selected through stratified random sampling. The data were collected using a validated adapted survey questionnaire, a writing test, and an oral interview. The collected data were analyzed using mean and standard deviation. The results indicated that the student-respondents frequently employ language alternation, particularly by inserting short Filipino or English expressions during discourse. They also regularly used language alternation for clarification, comprehension, identity, affective purposes, and lesson-related concerns. In terms of oral language proficiency, majority of the student-respondents were identified to be at the Intermediate English level (B1), while the written language proficiency is classified to be at the Elementary English (A2) level based on the Common European Framework of Reference for Languages (CEFR). The study suggests that language alternation is a common communicative strategy among senior high school students. Their language proficiency demonstrates the need for further enhancement.