Silicon crystallites produced by low-temperature plasma-enhanced chemical vapor deposition technique have been shown to have size-dependent photoluminescent and second harmonic generation responses. The crystalline volume fraction was estimated by Raman spectra and the grain sizes of crystallites were measured by X-ray diffraction. The structural chemical properties of poly-Si films were studied by means of Fourier-transform infrared spectroscopy and transmission spectrophotometry. The size and shape-dependent second-harmonic generation (SHG) of poly-Si films is also studied. The resonant SHG spectra show the fine structure with peak position at approximately 3.26 eV which is attributed to the response from Si-SiO2 interface (for aged films). The second resonant peak can be explained as the size-dependent SHG response from the bulk of nanocrystallites.