With the unprecedented development of the food industry, food preservatives have gained a leading role in food processing. In this study, investigations were carried out to assess the cytological effects of potassium metabisulphite (PMB) to onion (Allium cepa), one of the most used plants for determining the cytotoxic and genotoxic effects of different chemicals. Meristematic roots of A. cepa were treated with PMB solutions in different concentrations, ranging from 10 mg/l to 35 mg/l for 6, 12 and 24 h alongside an untreated control. The quantified parameters for the different concentrations of the PMB were mitotic index (MI %), mitosis phases index (PI %) and total abnormalities index (TAI %) meaning chromosomal aberrations and nuclear abnormalities. The results indicated that PMB reduced MI in A. cepa with increasing the concentrations and time exposure as compared with the untreated control. Thus, at concentration of 10 - 35 mg/l PMB, these values were reduced from 8.34% to 4.81% (6 h); 7.18% to 2.35% (12 h) and 4.12 to 1.43 (24 h). Also, the TAI value increased with increasing PMB concentrations and time: 0.51% to 9.98% (6 h), 7.11% to 19.84% (12 h) and 17.79 to 41.21 (24 h). The types of abnormalities induced by PMB in A. cepa meristematic cells were micronucleus, C-metaphase, star anaphase, stickiness, laggards, fragments, binucleated cells and pulverised nucleus. These alarming findings indicate the cytotoxic and genotoxic effect of PMB to A. cepa and suggest necessity to adopt more natural alternatives for food preservation in the future.