Hexagonal boron nitride (hBN) is a highly stable dielectric ceramic that has high thermal conductivity and is the softest one among the other BN forms. Although hBN is a suitable candidate for potential nanofluid applications, studies regarding hBN nanofluids are very limited. This study focuses on stability and thermal conductivity enhancement of hBN-DI water nanofluids. A two step method based preparation process relying on ultrasonication and use of surface active materials is developed to attain well dispersed, stable nanofluids. DI water based nanofluids, containing hBN nanoparticles, with a mean diameter of 70 nm, with different volume fractions are prepared using the developed process. The stability of the hBN-water nanofluids is determined either by quantitative methods such as time dependent zeta potential measurements and thermal conductivity measurements, or qualitative methods such as imaging with SEM (Scanning Electron Microscopy) and STEM (Scanning Transient Electron Microscopy). Following the investigation of the effect of several parameters, such as sonication time, optimum surfactant amount of the suspension on the stability of the nanofluids, thermal conductivity enhancement of nanofluids are investigated experimentally. The measured results indicate that the nanofluids have remarkably higher thermal conductivity values than the base fluid depending on the volume concentration of dispersed nanoparticles.