The present invention provides a polymerizable composition comprising (A) a compound including a polymerizable unsaturated group and (B) a macromolecular compound including, at a side chain thereof, a structure represented by the following general formula (I): Z.sup.-M.sup.+ General formula (I) wherein Z.sup.- represents COCOO.sup.-, COO.sup.-, SO.sub.3.sup.-, or SO.sub.2--N.sup.---R where R represents a monovalent organic group and M.sup.+ represents an onium cation. The present invention also provides a negative type planographic printing plate precursor responsive to an infrared laser, the precursor being superior in recording sensitivity and printing durability and using the polymerizable compound as a recording layer.