The formation of hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) from the reaction between methylidyne (CH) and acetonitrile (CH3CN) has been investigated by the Density Functional Theory (DFT) using the B3LYP functional in conjunction with the 6-311 ++G(d,p) and 6-311 ++G(3df,2p) basis sets. The authors have mapped the potential energy surface in detail, identifying two main entrance channels. In particular, the methylidyne radical attacks to the two different C atoms of the acetonitrile molecule. The results also show that hydrogen cyanide or hydrogen isocyanide can be formed by four possible pathways and that the product of C2H3 + HCN is the most favorable.