Block copolymer-polymer derived ceramic (PDC) precursor nanocomposites were prepared using amorphous poly(isoprene-block-(dimethylamino)ethyl methacrylate) (PI-b-PDMAEMA) and semicrystalline poly (isoprene-block-ethylene oxide) (PI-b-PEO) block copolymers as structure directing agents for poly(ureamethylvinyl)silazane (PUMVS). Studies on hybrid morphologies were performed using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). In the amorphous system, the PUMVS preferentially swells the PDMAEMA, and a systematic increase of the PUMVS to PI-b-PDMAEMA weight ratio resulted in lamellar, hexagonally packed cylindrical and body-centered cubic packed spherical morphologies. Crystallization of PEO in PI-b-PEO/PUMVS hybrids led to crystalline lamellar morphologies over a large range of PUMVS to PI-b-PEO weight ratios. The d-spacing of the PI-b-PEO/PUMVS hybrids increased only slightly upon PUMVS loading, because the strong chain stretching in the PI block is progressively relaxed as the PUMVS swells the PEO. Annealing of the PI-b-PEO/PUMVS system at elevated temperatures led to suppression of the PEO crystallization, resulting in order-order phase transitions.