Ethyl(nitrosyl)ruthenium [TpRuCl(Et)(NO)] (2) was isolated from the reaction of [TpRuCl(2)(NO)] (1) with LiBHEt3. NO insertion of 2 was observed from heating a solution of 2. In the presence of PPh3, nitrosoethane complex [TpRuCl-{N(=O)Et}(PPh3)] (3) was isolated, but the absence of PPh3 led to nitrosoethane-bridged dimer [(TpRuCl)(2){mu-N(=O)Et}(2)] (6). Also, in complex 3, conversion of the nitrosoethane moiety to acetaldoxime and acetonitrile was observed.