Novel single-source-precursors (SSPs), namely carbon nanotube modified poly (methylvinyl) silazane (CNTs-HTT 1800), were synthesized via amidation reaction of poly (methylvinyl) silazane (HTT 1800) with carboxylic acid functionalized carbon nanotubes (CNTs-COOH) at the assistance of ZnCl2 catalyst, which was confirmed by means of Fourier transform infrared spectra (FT IR) and transmission electron microscopy (TEM). Besides, the TEM results unambiguously show the homogeneous distribution of the CNTs in the matrix of SSPs while serious aggregation of the CNTs in the matrix of physically-blended-precursor. Crack-free monolithic silicon carbonitride modified by carbon nanotubes ceramic nanocomposites (CNTs-SiCN) were prepared through pyrolysis of the obtained SSP green bodies at 1000 degrees C. Due to the strong influence of polymer structure on the microstructure of final ceramics, the SSP-derived CNTs-SiCN nanocomposites clearly show the homogeneous distribution of the CNTs in the SiCN matrix while the physically-blended-precursor derived CNTs-SiCN nanocomposites exhibit serious aggregation and entangling of the CNTs in the SiCN matrix. With the same CNT content in the feed, the SSP-derived CNTs-SiCN nanocomposites possess significant improvements of electromagnetic (EM) absorbing properties compared to those from physically-blended-precursors, due to the quality of the dispersion of CNTs in the ceramic matrices.