Metallographic study has been carried out on the Nd-Fe-Co-B alloys to clarify the change in coercivity with the Co composition substituted for Fe in the Nd2Fe14B type sintered magnets. The decrease in coercivity caused by the Co substitution is attributed to the formation of soft-magnetic phases such as Nd(Fe, Co)2and Nd(Fe, Co)3. The mole ratio of Nd to (Fe+Co) of these soft-magnetic phases decreases with increasing the Co substitution. The Co concentration is much higher in these soft-magnetic phases than in Nd2(Fe, Co)14B matrix. The A1 addition in Nd-Fe-Co-B magnet makes the Nd(Fe, Co)2compound unstable to form the non-magnetic Nd3(Fe, Co, Al) compound, resulting in the increase in the coercivity of Nd-Fe-Co-B magnet.