Voltage gated potassium channels play critical roles in determining the responses of auditory brainstem neurons to acoustic stimuli. In the present study, we examined the developmental expression of potassium channels in rat cochlear nucleus. Quantitative RT-PCR revealed that Kv1.1 , Kv1.2 and Kv3.1 showed a monotonic increase in mRNA levels from postnatal days 3-28 (P3-P28), after which mRNA level was relatively constant until P56. In contrast, Kv4.2 mRNA levels were lower on average by a factor of 2 after P28 than before P28. Relative to Kv1.1, Kv3.1 and Kv1.2 mRNA were more abundant before P10 and less abundant thereafter. To address the relationship between message and protein levels, we performed semi-quantitative Western blotting for Kv1.2. The message for Kv1.2 increased earlier in development than the protein levels. Immunocytochemistry revealed a broad expression of Kv1.1 and Kv1.2 in the VCN. Staining intensity increased from 7-28 days postnatal. Kv1.2 immunostaining was less variable across cells than Kv1.1 staining. We conclude that maturation of potassium channel expression in the rat cochlear nucleus continues until at least 4 weeks postnatal.