Atomically thin monolayer molybdenum disulfides (MoS2) with tunable electronic structure has promising applications in opto-electronic devices and sensors. In this work, unique nano-patterning and surface oxidation of monolayer MoS2 was achieved based on hydrogen peroxide (H2O2) treatment. It was found that the exfoliated monolayer MoS2 can be uniformly oxidized when exposed to low-concentration H2O2, forming an intermediate phase composed of MoSxOy. In addition, patterned triangular pits with well-defined edges can be formed under high-concentration H2O2 condition. The band gap of monolayer MoS2 could be effectively modulated by H2O2 treatment as verified by photoluminescence spectra. This work shows that simple H2O2 treatment can be an alternative approach for both surface functionalization and band gap modulation of MoS2 flake, and it also provides an alternatively simple way to obtain patterned MoS2 nanostructures without complicated standard lithography processes. (C) 2018 Elsevier B.V. All rights reserved.