To prevent losses before consumption due to the rapid ripening of bananas, turning unripe bananas into flour and using it in bakery products can both enhance the functional properties of the product and transform bananas into a high-value product. In this study, it is aimed to enhance the functional properties of banana flour through fermentation, thereby investigating its potential use in the production of healthy snack biscuits which are widely consumed, especially by children and busy people. Different proportions (0%, 15%, and 30%) of unripe banana flour (UBF) and fermented unripe banana flour (FUBF) were added to biscuits, evaluating their impact on physical (color, diameter, thickness, spread ratio), textural (hardness), and functional properties (total phenolic content, antioxidant activity, dietary fiber, glycemic index). The effect of FUBF on biscuit spread ratio compared to UBF was positive (p < 0.05). The addition of UBF or FUBF significantly increased total phenolic content (TPC) and antioxidant activity (p < 0.05), with the highest TPC (1167.88 mg GAE/kg) observed in biscuits containing 30% FUBF (p < 0.05). Fermentation showed no significant effect on antioxidant activity of samples (p > 0.05). The glycemic index (GI) values were notably high across all samples, with the control at 78.59 and the 30% FUBF sample at 72.74 (p < 0.05), indicating all samples fell into the high GI food category. Biscuit hardness decreased significantly with UBF or FUBF addition (p < 0.05), while fermentation had no significant impact on hardness (p > 0.05). This study underscores the potential of UBF or FUBF to contribute to healthier snack options with improved functional characteristics.