Highly-porous and -uniform spherical nanoassemblies comprising a variety of Pt and Pd bimetallic primary nanostructures have been successfully synthesized via a facile chemical reduction approach with the assistance of a face-centered-cubic packed tri-blocking copolymer, Pluronic F127 (PEO₁₀₀PPO₇₀PEO₁₀₀), which not only acts as the spherical micro-reactors for keeping unique assembling dimensions, but significantly influences the reduction dynamics as well as the morphology of building blocks. Building blocks with elliptic, slender and flat petal like morphologies can thus be achieved by means of the precisely controlled atomic ratio of Pd/Pt and respectively exhibit distinct UV-visible extinction spectra. According to the characterizations of high-resolution transmission electron microscopy, high angle annular dark field images, energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy, we evidently identify that the central part of the present very special spherical nanoassemblies is Pd rich whereas the outer shell is Pt rich, mainly resulted from the difference in reduction potential for these two precursors. The detecting limitation of malachite green oxalate utilizing surface-enhanced Raman scattering (SERS) technique could approach 1 ppm or less for the flat petal like specimen. We believe that the newly designable metal growth approach described here will trigger the facile fabrication of advanced multi-metallic nanoassemblies with craving properties in the near future.