Several organic isocyanides have been observed so far in ISM (HNC, CH_3_NC, HCCNC). However there is still a lack of high-resolution spectroscopic data on simple iso- cyanides that could provide a basis for their detection. Diisocyanomethane (NC-CH_2_-CN) is a small molecule having only 7 atoms and being an interesting candidate for astrophysical detection. Rotational spectrum of diisocyanomethane has never been studied before. We measured the rotational spectrum of diisocyanomethane in the frequency range 120-620GHz using Lille fast-scan and solid-state source spectrometers. The spectroscopic study was supported by high-level theoretical calculations on molecular structure and both harmonic and anharmonic force field. The ground and the first excited vibrational state (v15) were assigned and analyzed. The dataset is composed of more than 2000 measured and fitted lines allows accurate predictions of transition frequencies of diisocyanomethane in the range up to 900GHz. The statistical analysis of the results of the fit shows that the use of S-reduction of Watson rovibrational Hamiltonian for spectral modelling is more appropriate.