The present study was concerned with the effect of the spatial attention on the processing of color and semantic information from a psychophysiological point of view. Event-related potentials were recorded from eight subjects during the color discrimination task and the category decision task under the condition where subjects attended to left or right visual field. Stimulus words were colored with red or green ink, and represented one of two types of semantic categories, that is, living things and inanimate objects. One of these stimuli was flashed in random order to the left or right in visual field. In The color discrimination task, the subjects required to detect the target according to the predetermined color and the spatial location. In the category decision task, subjects required to detect the target according to the semantic category and the spatial location. It was shown that the negative deflections, as reported by Harter et al. (1982), were elicited by stimuli at an attended location. Moreover, the earlier potion of this negativity (150-250 ms) was associated with attending to the locaton of the stimulus, the later portion of it (250-350 ms) was primarily associated with attending to one of the different types of stimuli presented at the attended location. These results were discussed from the view point of the early selection theory of attention.