A novel one-pot synthesis strategy has been developed to prepare organic modified LiFePO4/C nanocrystals under organic molecules assisted supercritical water (SCW) conditions. Powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) results indicate that crystalline LiFePO4 nanocrystals are formed under SCW conditions. The smallest ever reported LiFePO4 nanocrystals with size ca. 15nm are obtained by one-pot synthesis at 400°C in short reaction time. The SCW conditions along with suitable surfactants facilitated the in situ organic modification of LiFePO4 with controlled particles size. Further, addition of CNT during the SCW synthesis helps in developing conductive carbon coating on the surface after heat treatment.