Polymeric micelles that are composed of synthetic polymers are generally size controllable and can be easily modified for various applications. Lactosomes (A3B-type) are biodegradable polymeric micelles composed of an amphipathic polymer, including three poly(sarcosine) blocks and a poly(l-lactic acid) block. Lactosomes accumulate in tumors in vivo through the enhanced permeability and retention (EPR) effect, even on frequently administering them. However, lactosomes cannot be efficiently internalized by cells. To improve cellular uptake of lactosomes, cell-penetrating peptide (CPP)-modified lactosomes were prepared. Seven CPPs (including EB1 and Pep1) were used, and most of them improved the cellular uptake efficiency of lactosomes. In particular, EB1- and Pep1-modified lactosomes were efficiently internalized by cells. In addition, by using CPP-modified and photosensitizer-loaded lactosomes, we demonstrated the photoinduced killing of mammalian cells, including human cancer cells. Accumulation of the EB1-modified lactosomes in NCI-N87 tumors was shown by in vivo imaging. Thus, this study demonstrated that the CPP-modified lactosome is a promising drug carrier.