Arsenic toxicity may lead to skin manifestations and arsenic accumulation in keratinised tissue. Thus human keratinocytes has been extensively used to study dermal effects of arsenic exposure. The present study was aimed to investigate time and dose-dependent effects of arsenic using HaCaT cell line. Another major focus of the study was to evaluate if treatment with monoisoamyl dimercaptosuccinic acid (MiADMSA) offers protection against arsenic-induced oxidative stress and apoptotic cell death using HaCaT cells. HaCaT cell lines were incubated to three different concentrations of arsenic (10, 30 and 50 μM) for 24 h to identify the toxic dose by measuring oxidative stress variables. Later, MiADMSA pre-incubation for an hour preceded arsenic exposure (30 μM). We evaluated cell morphology, lactate dehydrogenase, glutathione linked enzyme and antioxidant enzyme activities to measure oxidative stress status, while MTT assay and caspase 9 and 3 levels were determined for cell viability and apoptotic status. The present study suggests arsenic-induced toxicity in a concentration-dependant manner. Arsenic also caused a significant increase in lactate dehydrogenase accompanied by an elevated antioxidant enzyme activities (superoxide dismutase, glutathione peroxidase and caspase activity). Interestingly, pre-treatment of cell with MiADMSA elicited significant protection against arsenic-induced oxidative stress and apoptotic cell death. The present findings are of clinical relevance and suggest MiADMSA to be a promising candidate in protecting skin against arsenic-induced toxic effects, which need further exploration using in vivo experimental models.