Post-translational modifications (PTMs) may affect the functions of human serum albumin. Here we review reports of novel PTMs of human serum albumin. This study reviewed one hundred twenty-three recently reported novel O-phosphorylation, glycation, methylation, carbonylation, and acetylation of albumin. Furthermore, the potential impact of these PTMs on albumin functions is discussed. Knowledge of these PTMs of albumin is important for the use of albumin in medical applications, e.g., in transfusion, drug formulations, and remedies.