Immunoglobulin G (IgG) is a class of monoclonal antibodies (mAbs) commonly produced in mammalian cell lines. These cell lines are grown in finely adjusted culture media, which contain components that may impact glycoforms. As variation of N-glycoforms can impact the biological properties of IgGs, medium composition should be controlled. Here, we studied the effects on IgG N-glycoforms of different components in hybridoma culture media, specifically compared bovine serum albumin (BSA) with other small molecules, using a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight multistage mass spectrometry (MALDI-QIT-TOF MSn)-based approach. We show that small molecular additives caused little change in glycan species, though a number of these reagents, especially glutamine, affected levels of glycosylation. In comparison, the addition of macromolecular protein BSA significantly changed IgG N-glycan patterns, not only in species but also in glycosylation levels. Together, our finding suggests that BSA increases the complexity of IgG N-glycoforms, thus raising the difficulty in maintaining glycoforms consistency during antibody production. Therefore, the effect of BSA on IgG N-glycans should be considered when designing optimal medium formulations for IgG production. KEY POINTS: ? Small molecular medium additives only affect glycosylation levels of IgG N-glycans. ? BSA significantly changes IgG N-glycoforms as a medium additive. ? BSA's skewing of IgG N-glycoforms should be considered in IgG production.