Introduction: Estimating the dietary and nutrient intake is one of the indirect methods of assessing nutritional status. Diets of adolescent girls in developing countries including Ethiopia are low in diversity, mostly consuming cereals with limited animal source foods and essential nutrients that led to malnutrition. The problem is highly exacerbated at adolescent stage, which exhibited rapid physiological changes. Hence, this study aimed to assess dietary diversity and associated factors among high school late adolescent girls in Tegede district.Methods: A school based cross-sectional study was conducted on 400 systematically selected adolescent girls from January to February 2018 in Tegede district high schools. Dietary diversity score was measured using a validated 24-hour dietary recall questionnaire based on 10 food groups. Binary logistic regression was used and Bi-variable and multivariable analysis were used to identify factors associated with dietary diversity and 95% confidence interval and Odds Ratio (OR) was computed to assess the strength of association. Variables with 0.05 p-value in the multivariable analysis were taken as significantly associated with the dietary diversity score.Result: The proportion of adolescent girls who had adequate dietary diversity was 47.3% [95% CI: (42- 52%)]. Urban residences [AOR=6.60(3.90 11.16)], Living with family [AOR=5.53(3.26 9.37], common decision on food preparation at household level [AOR=1.97(1.14 3.39], school nutrition club member [AOR=2.33(1.34 4.05)] and access to home gardening (AOR=2.69[(1.57 4.62)] were significant determinants of adequate dietary diversity.Conclusion: This study indicated the proportion of adolescent girls who had diversified diet was low. Family residences, Students living status, decision in home food preparation, school nutrition club member and access to home gardening were significant associated factors. These finding underscored that strengthening of school nutritional club and home gardening is mandatory to curb nutritional related problems.