: Effective menstrual hygiene is vital to the health, wellbeing, dignity, empowerment, mobility and productivity of girls and women. The inadequate knowledge and improper practice of menstrual hygiene among various age group of girls and women may affect their reproductive health.A descriptive study was carried out with the objectives to assess the knowledge and practice on menstrual hygiene and to assess the significant association between selected Demographic variables with knowledge and practice among the girl students of Balika Vidya Mandir School, Digboi, Tinsukia, Assam. The study was conducted in Balika Vidya Mandir School, Digboi, Tinsukia, Assam, among 60 girl students selected by simple random sampling technique. A self structured questionnaire and a checklist was used to assess the knowledge and practice on menstrual hygiene. Both descriptive and inferential statistics were used to find out the result of the study.Findings related to knowledge revealed that majority 82% (49) girl students had moderately adequate knowledge, 10% (6) had inadequate knowledge and only 8% (5) had adequate knowledge on menstrual hygiene.Findings related to practice revealed that majority 75% (45) girl students had moderately adequate practice, 17% (10) had inadequate practice and only 8% (5) had adequate practice on menstrual hygiene. Findings related to association between knowledge and selected demographic variables revealed that there is significant association between knowledge and age of girl students and family income. Findings related to association between knowledge and selected demographic variables revealed that there is significant association between practice and family income and religion. From the study findings it can be inferred that knowledge and practice of girl students of the school have moderately adequate. Therefore more emphasis should be given on providing knowledge regarding menstrual hygiene among the girl students.