Understanding the build-up of stellar mass is one of the primary goals of extra-galactic astronomy. Various theoretical studies find that star formation activity for galaxies in high-density region peaks between redshift z=3-5, whereas for galaxies in the low-density environment it peaks between redshift z=1-2. I will present my work on how the environment affects the stellar mass build-up in galaxies. We measure the star formation histories of galaxies in a proto-cluster at z~2 in the COSMOS field using the Spectral Energy Distribution fitting module Prospector. We compare the relative star formation histories of galaxies at z=2 as a function of their environment, morphological type, and stellar masses. Our preliminary results suggest a minimal effect of the environment on the star formation histories with galaxies of similar stellar mass. This result is consistent with our previous environmental studies at z~2.