Two-dimensional (2D) materials have attracted great interest due to their unique structures and exotic properties related to promising applications and fundamental research. Reducing the dimensionality of 2D materials into their 1D nanostructure is also highly desirable for the exploitation of novel properties and offers new research opportunities. In this work, we demonstrate a bottom-up synthesis of molybdenum disulfides (MoS2) nanoribbons on graphene substrate via chemical vapor deposition (CVD) by precisely tuning the growth parameters into a sulfur-enriched condition. MoS2 nanoribbons are mainly formed from the CVD grown MoS2 flakes along the armchair (AC) direction. Atomic resolution ADF-STEM imaging characterizations show an alternating presence of molybdenum and sulfur zigzag edge terminations at the edges of MoS2 nanoribbons. While at the apex of the nanoribbon, sulfur terminated zigzag edges become dominant. Taking these results together, we revealed the underlying growth mechanism of MoS2 nanoribbons. Electronic transport properties of the MoS2 nanoribbons were also measured by fabricating back-gate-effect transistors (FETs). The nanoribbon FETs present n-type behavior with a current on/off ratio higher than 104 at V DS = 1 and a carrier mobility of 1.39 cm2 V-1 s-1. This work offers a new route to synthesize 1D MoS2 nanoribbons, which has great potential in fabricating other 2D materials-derived 1D nanostructures.