A wide variety of nanomedicine has been designed for cancer therapy. Herein, we describe the synthesis and evaluation of a hypoxia-responsive copolymer for siRNA delivery (Perche et al., Angew Chem Int Ed Engl 53:3362-3366, 2014). The synthesis is achieved using established coupling chemistry and accessible purification procedures. A polyelectrolyte-lipid conjugate (polyethyleneimine 1.8 kDa-dioleyl-phosphatidylinositol, PEI-PE) and polyethylene glycol 2000 (PEG) were assembled via the hypoxia-sensitive azobenzene (Azo) unit to obtain the PEG-Azo-PEI-DOPE copolymer. This copolymer can condense siRNA and shows hypoxia-induced cellular internalization and reporter gene downregulation in vitro and tumor accumulation in vivo after parenteral administration (Perche et al., Angew Chem Int Ed Engl 53:3362-3366, 2014). We also detail procedures to evaluate hypoxia-targeted polymers both in monolayer cultures, cancer cell spheroids and in tumor xenografts murine models.