The invention provides a polymerizable composition comprising: a binder polymer containing at least an acid group having an acid dissociation constant (pKa) of 5.5 or more and a radical addition polymerizable group, and a radical-generating compound capable of generating a radical with light or heat. Further, the invention provides a negative-working planographic printing plate precursor which has a recording layer containing the polymerizable composition. Use of the polymerizable composition of the invention provides a planographic printing plate precursor that is capable of forming high-quality images free from stains in non-image portions, and further has high strength in formed image portions and excellent printing endurance.