X-ray diffraction studies of face-centered-cubic metallic nanoparticles with different morphologies are discussed based on the experimental data and the calculation of the Debye equation with the truncated and perfect strain models. At least four basic morphologies frequently observed in face-centered-cubic metallic nanoparticles, namely sphere, cube, decahedron, and icosahedron, can be clearly distinguished from their characteristic integrated intensity ratios of the first two X-ray diffraction peaks, that is, (2. 0. 0) to (1. 1. 1).