Intracellular pH-regulatory mechanisms are acquired by growing mouse oocytes with meiotic competence, and these mechanisms become fully active when the oocytes develop to the germinal vesicle (GV) stage as shown in CF1 and Balb/c strains mice. On the other hand, there is some evidence showing that intracellular pH-regulatory mechanisms are inhibited at the stages of Metaphase I (MI) and II (MII) oocytes in the CF1 strain mouse and hamster. Since it has been shown that the intracellular pH regulatory mechanism can be functionally different among mouse strains (e.g., CF1, Balb/c), the aim of this study was to investigate the activity of HCO3-/Cl- exchanger (anion exchanger, AE), which protects cells against alkalosis during the meiotic maturation process, in the GV oocyte up to the pronuclear (PN) zygote derived from the Balb/c strain mouse. Intracellular pH (pH(i)) was recorded using a microspectrofluorometric technique during meiotic maturation stages. KSOM-based solutions were used as culture and recording solutions. AE activity was determined using a Cl- removal assay and was reported as the change in pHi per minute. AE activity was high in GV stage oocytes but was significantly inhibited at the MI and ME stages. AE activity was higher in the PN zygote stage. This activity was significantly inhibited in all oocyte and zygote stages by 4,4'-Diisocyanatostilbene-2,2'-disulfonic acid disodium salt. After alkalosis induction, the pHi of MI and MII stage oocytes did not completely recover; however, almost complete recover), occurred in the GV stage oocytes and PN zygotes. These results suggest that AE is inhibited during the meiotic maturation process in the Balb/c strain mouse.