Liposomal compositions comprising peptide epoxyketone compounds are described, as well as methods of making and using such liposomal compositions. These liposomal compositions enhance the therapeutic window of peptide epoxyketone compounds by improving in vivo half-life relative to non-liposomal compositions comprising peptide epoxyketone compounds, providing desirable pharmacodynamic profiles, and providing anti-tumor activity in a human tumor xenograft model, greater than or equal to non-liposomal compositions comprising peptide epoxyketone compounds. Further, experiments performed in support of the present invention demonstrated improved tolerability of liposomal compositions comprising peptide epoxyketone compounds.