An upper bound for the plastic collapse load of flat plates under uniformly distributed loads is studied. And, assuming that the deformations are convex at every parts, the minimum upper bound is determined by the following conditions. 1. Every deformed planes include edge lines. 2. Hinge lines are straight. 3. P=(∫_<s1>kMsds)/(I_1)=(∫_<s2>kMsds)/(I_2)……=(∫_<si>kMsds)/(I_i) P : Collapse load Ms=Mxsin^2φ+Mycos^2φ k=2 for fixed edges=1 for supported edges Ii=1/2∫_<si>r^2ds for fixed or supported edges =0 for free edges
