A surface treatment liquid capable of making a surface of a treatment target hydrophilic or hydrophobic without including a resin having a coating film formation property, and a surface treatment method using the surface treatment liquid. The surface treatment liquid includes a resin, a solvent and a strong acid having a pKa of 1 or less. The resin includes a functional group I that is at least one of a hydroxyl group, a cyano group, and a carboxyl group, and a functional group II that is a hydrophilic group or a hydrophobic group other than the functional group I.