To tackle the common issue of green defects in material extrusion (MEX) additive manufacturing (AM) cemented carbides, warm isostatic pressing (WIP) was introduced to eliminate defects of MEX WC-9Co cemented carbide greens, thereby improving both microstructure uniformity and mechanical properties of sintered bodies. The results indicate that WIP reduces defects in MEX greens, thus decreasing the dimensions and numbers of defects, modifying shapes of pores within sintered bodies, while preserving surface quality and shape characteristics. Compared with WC-9Co prepared via MEX followed by debinding and sintering (DS), the hardness of WC-9Co prepared using MEX-WIP-DS does not change significantly, ranging HV₃₀ 1494-1508, the transverse rupture strength increases by up to 49.3%, reaching 2998-3514 MPa, and the fracture toughness remains high, ranging 14.8-17.0 MPa·m^1/2. The mechanical properties surpass comparable cemented carbides fabricated through other AM methods and are comparable to those produced by powder metallurgy. The integration of green WIP into MEX-DS broadens the MEX processing window, and improves the overall mechanical properties of MEX AM WC-Co cemented carbides.