A facile and efficient method has been developed to produce high yield boron nitride nanosheets (BNNSs) by a combined strategy of quenching pre-heated hexagonal boron nitride (h-BN) in an aqueous solution and subsequent liquid exfoliation. The thermal and quenching stresses promoted the exfoliation of h-BN into BNNSs and subsequent sonication of the pre-stressed h-BN led to formation of BNNSs comprising of 2-3 layers. The products were BNNSs with a thickness of less than 2 nm that was confirmed by atomic force microscopy measurements. X-ray diffraction, transmission electron microscopy and scanning electron microscopy investigations revealed the structure and the sheet-like morphology of BNNSs. The elemental composition and chemical state of the surface was analyzed by X-ray photoelectron spectroscopy. The stable dispersibility of boron nitride in mixed solvent (ethanol/water) was confirmed via UV-vis spectrophotometry. This convenient strategy provides an extensive route to produce large-scale and high-quality BNNSs.