To provide a specific synthetic rubber latex and a moistureproof adhesive composition which uses the latex, is excellent in moistureproofness, and exhibits a small decrease in viscosity at a high shear rate.

The synthetic rubber latex is prepared by the emulsion polymerization of a monomer mixture comprising 0.3-10 wt.% hydroxyl-group-containing vinyl monomer and other copolymerizable vinyl monomers (the sum being 100 wt.%) in the presence of a reactive emulsifier and has a film formation temperature of its copolymer in the range of 0°C-20°C and a toluene gel fraction adjusted to 40%-90%. The moistureproof adhesive composition, excellent in moistureproofness and coating suitability, is prepared by compounding 100 pts.wt. (solid basis) above-prepared latex (A) with 0.1-10 pts.wt. (solid basis) wax emulsion (B) and 0.1-10 pts.wt. (solid basis) polyurethane resin (C).