The magnetization of Mn1-xCoxPt3 ordered alloys (x = 0.25, 0.4, 0.5, 0
.6, 0.75) has been measured from 10 to 300 K. The Curie point has a mi
nimum at x approximate to 0.5. The magnetization vs, temperature curve
of x = 0.5 has a maximum near 60 K under low fields. The anomalous te
mperature dependence of coercive force was also observed.