Gastric cancer is the second most common cause of death from cancer worldwide and resistant to various chemotherapeutic regimens. In gastric cancer, the anti-apoptotic Mcl-1 protein is expressed in up to 75% of all cases and associated with poor prognosis. The biological relevance of Mcl-1 expression in gastric cancer is unclear. Thus, we investigated the functional significance and potential role of Mcl-1 as a molecular target in gastric cancer by using an antisense strategy. Gastric cancer cell lines (NCI-N87, MKN-28, MKN-45) were treated with Mcl-1 antisense oligonucleotides. Protein expression, cell growth and apoptosis were assessed for single-agent Mcl-1 AS oligonucleotide treatment and for combinations with docetaxel or cisplatin. Treatment by Mcl-1 AS oligonucleotides resulted in approximately 50% reduction in Mcl-1 protein levels in all gastric cancer cell lines examined. Surprisingly, dose-dependent Mcl-1 downregulation produced a significant increase in apoptosis and up to 60% decrease in cell growth. Moreover, combination of Mcl-1 AS oligonucleotide with docetaxel or cisplatin displayed synergistic anti-tumor activity. In conclusion, the impressive single-agent anti-tumor activity and the synergistic effect of Mcl-1 AS oligonucleotides in combination with chemotherapy might qualify Mcl-1 as a promising molecular target for AS oligonucleotide based treatment strategies for gastric cancer in the future.