Background. Adolescent girls in developing countries do not have proper information, and proper information is covered up by sociocultural boundaries resulting in various morbidities. This study aimed to determine level of knowledge and its associated factors regarding menstrual hygiene amongst adolescent school girls in Dang district, Nepal. Methods. Institution-based cross-sectional study was conducted between April and October 2019 among 406 adolescent girls studying in grades 8–10 between ages of 10–19 years in Dang district, Nepal. From a total of 10 local units, 5 were selected randomly. Out of the selected 5 units, 10 schools consisting of 5 government and 5 private schools were selected through disproportionate stratified random sampling. A further 406 students were then selected randomly from the 10 selected schools. Bivariate analysis was used primarily to assess the association between dependent and independent variables. Variables which were associated with bivariate analysis were entered into a multivariable logistic regression model to identify associated factors of menstrual hygiene practice. Results. The mean age and family size were 15.13 ± 1.19 and 5.58 ± 1.81, respectively. A total of 87.7% of adolescents had good knowledge regarding menstrual hygiene. Adolescents living in rural area (AOR = 0.27, CI: 0.12–0.61,
p
≤
0.001
), private schools (AOR = 6.10, CI: 1.58–23.46,
p
≤
0.001
), mothers who can read and write (AOR = 0.22, CI: 0.07–0.64,
p
≤
0.001
), fathers who have up-to-grade-10 education (AOR = 5.15, CI: 1.84–14.39,
p
≤
0.001
), and living only with mothers (AOR = 0.29, CI: 0.12–0.69,
p
≤
0.018
) were significantly associated with level of knowledge of menstrual hygiene. Conclusions. Though the majority of respondents had a good level of knowledge regarding menstrual hygiene, there was a knowledge gap in specific areas. The level of knowledge was significantly poor among adolescents in rural areas and those living only with mothers. Thus, this study concerns the need for policy makers to focus on specific education regarding menstrual hygiene in rural areas including both parents.