The synthesis and characterization of the new phosphino acetylenes (C6H5) 2PC≍ CCF3,(C6H5) 2PC≍ CC (CH3) 3,(C6H5) 2PC≍ CP (C6F5) 2,(C6F5) 2PC≍ CCH3,(C6F5) 2PC≍ CC6H5,(C6H5) 2PC≍ CP [N-(C2H5) 2] 2, the mixed arsine-phosphine (C6H5) 2PC≍ CAs (C6H5) 2 and the arsino acetylene (C6H5) 2AsC≍ CCF3, are reported.