Abstract Biologically active peptides and proteins are novel agents that show promise in the development of anticancer drugs. Their relatively low cell permeability and poor tumor selectivity, however, impede their widespread applicability. In this study, we evaluated the tumor selectivity, cellular internalization, and biological activity of a cell-permeable ovarian cancer cell–specific therapeutic protein consisting of TAT-OSBP and constitutively active MKK6(E), an upstream kinase of the p38 signaling pathway that mediates cellular apoptosis. OSBP, a 7-amino-acid peptide with high affinity for human ovarian cancer HO8910 cells, was conjugated to the cell-penetrating peptide (TAT) to form a tumor-selective peptide (TAT-OSBP), which was further conjugated with EGFP or MKK6(E). Flow cytometry and fluorescent microscopy were performed to evaluate the tumor-targeted penetration of TAT-OSBP-EGFP. The inhibitory effects of TAT-OSBP-MKK6(E) were determined by cell proliferation and apoptosis assays. The internalization efficiency of TAT-OSBP-EGFP was significantly higher than that of TAT-EGFP. TAT-OSBP-EGFP selectively penetrated HO8910 cells. TAT-OSBP-MKK6(E) fusion protein inhibited cancer cell growth to varying degrees, with the highest level of inhibition in HO8910 cells. Moreover, TAT-OSBP-MKK6(E) significantly induced apoptosis of HO8910 cells. However, there was no significant difference in apoptosis in the normal ovarian epithelial cells treated with either TAT-OSBP-MKK6(E) or TAT-MKK6(E). Our results demonstrate that TAT-OSBP-MKK6(E) is a novel artificially designed molecule, which induces apoptosis and selectively targets human ovarian carcinoma HO8910 cells. Our study provides novel insights that may aid in the development of a new generation of anticancer drugs.