Including glycosylation, hydroxylation, acylation, disulfide bond formation, etc. Among them, glycosylation is the most important, and almost all protein synthesized on endoplasmic reticulum is eventually glycosylated. The functions of glycosylation are: ① to make protein resist the action of digestive enzymes; (2) endowing protein with the function of conducting signals; ③ Some proteins can be folded correctly only after glycosylation.

Endoplasmic reticulum can also participate in protein synthesis, folding, assembly and transportation of new peptide chains.