A method of producing a planographic printing plate support in which after aluminum is continuously cast directly from molten aluminum into a thin aluminum plate, the aluminum thin plate is subjected to cold rolling, heat treatment and flattening to obtain an aluminum support. The aluminum support is then subjected to surface toughening. The components of the aluminum support areFe: 0.4%-0.2%,Si: 0.20%-0.05%,Cu: not larger than 0.02%, and the Al purity is not smaller than 99.5%. After continuous casting, Fe in a range of from 20% to 90% of the Fe total content exists in a grain boundary and the rest of Fe exists as a solid solution in grains. In this case, it is preferable that in a section perpendicular to the direction of continuous casting, the grain size is in a range of from 2 .mu.m to 500 .mu.m.