Microglia are immunocompetent cells in the central nervous system that have many similarities with macrophages of peripheral tissues. Their activation protects local cells from foreign microbial infection in the CNS. However, “over-activated” microglia become a “Double-edged sword” which show neuronal toxicity and are implicated in a variety of neurodegenerative disease. Previous studies have suggested that potassium channels play a role in regulating microglial activation, migration and proliferation. However what kinds of potassium channel subunits are expressed in microglia, whether their expression changes after microglial activation and the functional role of most potassium channels expressed in microglia are poorly characterized. To address these questions, we used the N9 mouse microglial cell line as a cell model for experiments in vitro. Lipopolysaccharide (LPS), which is the endotoxin of gram negative bacteria, was used to stimulate microglial activation that results in subsequent nitric oxide (NO) release. Using qRT-PCR, we analyzed mRNA expression of >80 potassium channel pore-forming subunits and their regulatory subunits in both LPS-treated (1μg/ml for 24h) and untreated microglia. In resting microglia, Kv3.3 channel mRNA was most abundant with other mRNAs for other channels previously reported in microglia, such as the large (BK) and intermediate (IK) conductance calcium-activated potassium channels, and the voltage gated Kv1.3 and Kv1.5 channel mRNA, expressed at a lower level. The mRNA expression of some channel subunits changed significantly after LPS treatment. For example, mRNA expression of K2p6.1 and IK was decreased by 34±4.1% and 53±15.8% respectively whereas Kv1.3 mRNA expression was was increased by 194±18.3%. These data suggested that LPS-induced changes in channel mRNA expression may be involved in microglial activation. We examined whether pharmacological manipulation of these channels controlled LPS-induced NO release. We found that the IK selective blocker, Tram-34 (1μM) and the Kv1.5 inhibitor propafenone (PPF) (10 μM) significantly decreased LPS-induced NO release by 9±1.2% and 12±0.9% respectively. Ba2+ (1 mM) that inhibits inwardly rectifying potassium channels as well as K2p6.1 also significantly attenuated LPS-induced microglial activation by 13±1.7%. Inhibition of Kv1.3 channels using margatoxin had no significant effect on LPS-induced NO release. Inhibition of BK channels by paxilline had no significant effect alone however, paxilline attenuated the effect of Tram-34, PPF and Ba2+ to control LPS-induced NO release. In this study, we characterized the potassium channel mRNA expression pattern in N9 mouse microglia. IK, Kv1.5 channels but not Kv1.3 were implicated in regulating LPS-induced microglial NO release. In addition, BK channels may work as a modulator regulating the effect of other channels on NO release by activated microglia.