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Magnetic, electronic transport and magneto-transport behaviours of (Co1-xMnx)(2)P (0.55 <= x <= 0.675) compounds have been systematically investigated. A typical metallic-conductivity behaviour is observed in the ferromagnetic compound (Co0.45Mn0.55)(2)P. The increase in the Mn concentration gives rise to dramatic changes in magnetic, electronic transport and magneto-transport behaviours. With increasing temperature, a first-order phase transition from antiferromagnetism to ferromagnetism takes place at about 145 K, 185K and 240K for x = 0.60, 0.625 and 0.65, respectively. (Co0.4Mn0.6)(2)P and (Co0.375Mn0.625)(2)P compounds experience a metal-insulator transition (Anderson transition) with decreasing temperature. An external magnetic field of 5 T strongly influences the Anderson transition, lowering the transition temperature from 80 to 55K for (Co0.4Mn0.6)(2)P and from 115 to 70K for (Co0.375Mn0.625)(2)P. In contrast with this metal-insulator transition, an insulating behaviour appears in the temperature range from 10 to 300K for (Co0.35Mn0.65)(2)P and (Co0.325Mn0.675)(2)P compounds. Below the antiferromagnetic-ferromagnetic transition temperature TAF-F, a metamagnetic transition can be induced by an external magnetic field. The metamagnetic transition is accompanied by a maximum magnetoresistance ratio of -7%, -6.3% or -3.7% at 5 T in the (Co0.4Mn0.6)(2)P, (Co0.375Mn0.625)(2)P or (Co0.35Mn0.65)(2)P compound at 10 K. The mechanisms of magnetoresistive behaviours are discussed in terms of the formation of a super-zone gap in the antiferromagnetic state.