We propose a simple optical technique to measure time-resolved nanoscale surface profile of an evaporating sessile fluid droplet. By analyzing Newton ring like high contrast fringes we demonstrated /100≈5 nm sensitivity in surface height change of the air-water interface. This allowed us to precisely measure transient surface dynamics during the contact-line slips, weak perturbations on the evaporation due to external magnetic field and partial confinement of the drop. Further, we demonstrate wide applicability of this technique by measuring the nanoscale surface dynamics of the water drop resting on a deformable oil interface. OCIS codes: (120.6650) General; (240.6648) The evaporation of water drops is common phenomenon with many applications. It finds technological applications in printing [1, 2] cooling of electronic devices [3] and in micro-lithography on biomaterials [4]. The evaporation rate is very sensitive to small impurities in fluids, external electric and magnetic fields, as well as substrate properties [5]. Its nanoscale measurement is essential to better understand the behavior of evaporating drop in various circumstances. Previous measurements on evaporation of fluid drops employed diverse techniques such as gravimetric measurement of mass-loss using quartz crystal micro balance [6]. Raman thermometry[7] and atomic force microscopy cantilevers [8]. Various optical techniques have also been used such as microscopic imaging of the drop [9, 10] fiber-optic sensing [11] light scattering from fiber suspended drop [12] reflectometry [13] and twobeam Mach Zehnder interferometry [14]. However, few techniques offer nm resolution for in situ measurement of surface height change due to evaporation. During evaporation of a sessile drop from a solid substrate, its contact-line could slip due to imbalance of interfacial stresses. This leads to fast nanoscale surface instabilities [15,16]. Many theoretical studies exist [17,18] however, time-resolved measurements of slipping events with few nm precision have not been demonstrated yet. Moreover, measurement of surface dynamics of an evaporating drop resting on soft deformable substrate (water drop on oil) is also of great recent interest [19,20]. Therefore, a simple optical technique offering time-resolution, precision, and flexibility to probe such diverse situations is desired.In this paper, we show that by analyzing high-contrast Newton ring like fringes one can dynamically resolve nanometric surface changes in an evaporating water drop. A resolution of /100≈5 nm in its height at (0.01-160 nm/s) rate was demonstrated. This high sensitivity allowed us to measure nanoscale surface dynamics when the contact line slipped on a glass substrate [21]. Applications of the technique to measure perturbations on the evaporation rate by static magnetic field, by partial confinement of the drop, and evaporation dynamics of a water drop resting on a soft deformable substrate are demonstrated. The schematics of our experimental setup are shown in Fig. 1. Two complementary arra...