We investigated characteristics of identified GABAergic neurons in slices of the superficial superior colliculus (sSC) using transgenic mice in which green fluorescent protein (GFP) is specifically expressed in GABAergic neurons. Whole-cell patch clamp recordings and intracellular staining with biocytin revealed electrophysiological and morphological properties of GFP-positive neurons. GFP-positive neurons had a tangentially elongated wide dendritic field. In response to depolarizing current pulses, most of the GFP-positive neurons showed either of two firing properties; 55% (n=36/65) generated successive spikes with a constant firing frequency and 22% (n=14/65) showed transient burst firing at a threshold level for spike generation. These results elucidate a functional heterogeneity of GABAergic neurons, and provide fundamental information to understand the function of the GABAergic system in the sSC.