Purpose <p>Using biopesticides, like <i>Beauveria bassiana</i> is a crucial method used in biological pest control programs. <i>Beauveria bassiana</i> is a widely used entomopathogenic fungus in biological pest control programs. The lab culturing of <i>B.bassiana</i> requires a growth medium containing different nutrients for fungal growth, such as polydextrose agar (PDA). The high cost of PDA and similar growth media opens the door toward finding a low-cost alternative growth medium. As an agricultural waste, banana peels powder BPP contains a lot of nutritional compounds, such as C, O, N, and P, proteins, sugars, and fatty acids, which are essential for fungal growth.</p> Methods <p>In this study, BPP normal-sized particles, nano-sized particles BPN, and their aqueous and alcoholic extracts were evaluated as a sustainable, cost-effective, alternative growth medium for <i>B.bassiana</i> compared with PDA. The prepared BPP and BPN were characterized using XRD, FTIR, BET analysis, SEM–EDX, Zeta-size and potential, and UV–Visible spectroscopic analysis. Statistical analysis using two-way ANOVA, cost-effectiveness analysis, and the plate counting technique were performed.</p> Results <p>The present study revealed 7.5 times more cost-effectiveness for BPP samples than PDA, and an average growth of 22 CFUs/ plate for BPP samples compared with 12.67 CFUs/ plate in the case of PDA.</p> Conclusion <p>The present work strongly supports using banana peels and agricultural waste as a value-added, alternative, cost-effective growth medium for <i>B.bassiana</i> fungus, and recommends future research on using banana peels and other agricultural wastes as a sustainable growth medium for other microbial species.</p> Graphical Abstract <p></p>