Abstract: In this study, dose-dependent effects of lunularic acid (LA) on some physiological, cytogenetic, biochemical and anatomical parameters were investigated in Allium cepa L. bulbs. For this purpose, physiological parameters to be analyzed experimentally: germination percentage, root length, root number and fresh weight; cytogenetic parameters: micronucleus (MN) frequency, chromosomal aberrations (CAs) and mitotic index (MI); biochemical parameters were determined as catalase (CAT), superoxide dismutase (SOD) activities, malondialdehyde (MDA) level and free proline (Pr) content. In addition, cross-sections were taken from the roots and structural changes in meristem cells were examined. Onion bulbs were divided into four groups as one control and three treatments. The bulbs of the control group were kept in cuvettes containing tap water and the bulbs of the treatment group were kept in cuvettes containing 1, 5 and 10 mM LA for 7 days. LA administrations caused a decrease in all investigated physiological parameter values, an increase in the frequency of MN and CAs, and reduce in MI compared to control group. In addition, LA application caused dose-related increases in CAT and SOD activities and MDA and Pr levels compared to control group. LA application promoted CAs such as sticky chromosome, spindle fiber damage, vagrant chromosome, reverse polarization in root meristem cells. After all LA applications, root anatomical structure changes such as epidermis cell deformations, flattened cell nucleus and unclear transmission tissue were observed and it was determined that these changes reached a maximum at 10 mM LA dose. As a result, it has been understood that high doses of LA promote multi-directional toxicity and the Allium test is a very reliable test in determining this toxicity.