Bcl-xL is an apoptosis inhibitor that is upregulated in bladder cancer (BCa) and provides an attractive target for molecular therapies. Treatment with specific antisense oligodeoxynucleotides (AS‑ODNs) or small interfering RNAs (siRNAs) were able to sensitize BCa cells to conventional chemotherapeutics. Ten new Bcl‑xL‑targeting AS‑ODNs were systematically designed by using predicting software. AS‑BX2034 and AS‑BX2100 as well as the previously optimized siRNA construct si‑BX713 were selected for further detailed in vitro analysis in the BCa cell lines UM‑UC‑3 and EJ28. Bcl‑xL mRNA and protein expression levels, cell viability and apoptosis were examined 72 h after transfection. A single treatment with AS‑BX2034 or AS‑BX2100 caused only a low inhibition of the Bcl‑xL mRNA expression with the highest reduction of ≤20% in UM‑UC‑3 cells. In contrast, a single treatment with si‑BX713 strongly decreased Bcl‑xL mRNA expression level by ≤69% in UM‑UC‑3 cells and by ≤86% in EJ28 cells. Both gene expression inhibitor types induced a low to moderate reduction of viability. Depending on the cell line, a combined treatment with AS‑BX2100 or si‑BX713 and cisplatin (CDDP) caused an additional inhibition of cell viability by ~33 and 38%, respectively, compared to the respective control construct combined with CDDP. In comparison to the respective control treatment, combinations of AS‑BX2100 and CDDP led to a stronger induction of apoptosis by 57% in UM‑UC‑3 cells and 44% in EJ28 cells, whereas the combination of si‑BX713 and CDDP enhanced apoptosis by 38 and 118% in UM‑UC‑3 and EJ28 cells, respectively. Our comparative studies showed a stronger knockdown of Bcl‑xL by the siRNA construct compared to AS‑ODN treatment in both BCa cell lines. In combinatory treatments, the Bcl‑xL-directed siRNA markedly enhanced the anti-proliferative and apoptotic effects of CDDP and therefore, may serve as suitable tool for chemosensitization of BCa cells.