At the final maturation process red blood cells (RBC) are enucleated, becoming unable to synthesize nucleic acids as well as proteins. RBCs survive approximately 120 days in circulation using glucose as the sole energy source. Most crucial RBC functions depend on ATP to sustain physiological homeostasis. It is thus quite important that generation of ATP by glycolysis and replenishing of adenine nucleotide pools by the reaction, which is catalyzed by adenylate kinase (AK1). In turn, ribosomal RNA is degraded during remodeling of reticulocytes, and pyrimidine ribonucleotides become unnecessary for RBC viability. Thus they should be dephosphorylated by pyrimidine 5'-nucleotidase (P5N-I) and finally transported outside RBCs. There have been reported that hereditary deficiency of AK1 and P5N-I may cause shortened RBC life span, i.e. hemolytic anemia. In this review, we summarize physiological importance of these enzymes, which are involved in ribonucleotides metabolism during RBC maturation.