Researchers investigated the resource allocation of the spatial scale of visual attention in using the classic 'cue-target' paradigm that was adopted in order to enable subjects to identify a target. Behavioral result showed that target detection in attended areas is facilitated by the cue to target location. Electrophysiological data indicated that the early ERP components of P1 and N1 are probably related to the processing of the spatial scale in visual attention. Here, it should be noted that the effect on the spatial scale of visual attention without spatial cue remains unclear. Using the experimental paradigm of 'without spatial cue', this study investigated electrophysiological correlates of the resource allocation within the different spatial scale of visual attention. Event-related brain potentials were recorded for the appearance of target stimuli with which participants were required to respond quickly to the incoming stimuli during three conditions (visual angles of diameter were 3.2°, 6.4°, and 9.6°) of spatial position that the target stimuli appeared randomly. Additionally, the 'warning'(without any hint on the spatial information) is just remind the participants that the target stimuli might be appeared after an interval with a randomly varying duration between 0.8 and 1.2 s. As paid volunteers, seventeen healthy undergraduates (8 males and 9 females, age 21-26, M=24.3 years) were recruited to take part to this study. The participants in the experiment were all right-hand, had normal or corrected-to-normal vision and had no neurological or psychological disorders. This study was approved by the local ethics committee, and all participants signed an informed consent form prior to their inclusion in the experiment. The behavioral data showed that the mean reaction times (RTs) of detecting the target stimuli for the three spatial positions were 3.2° (M=494ms, SD=64), 6.4°(M=518ms, SD=72), and 9.6°(M=552ms, SD=74). The repeated measures analyses of variance (ANOVA) indicated that mean RTs were shorter for 9.6°than for 3.2°(p<0.0001) and 6.4°(p<0.0001), and mean RTs of 6.4° were also shorter than the case of 3.2°, which indicates that the RTs on detecting a stimulus in unfixed position decreased significantly with the increase of visual angle. ERP results indicated that the N1 amplitude was higher for 3.2°(M= -5.622 ?V, SE=0.927) and 6.4°(M= -5.209 ?V, SE=0.855) than for 9.6°(M= -4.592 ?V, SE=0.808) between 160 and 200 ms after onset of the target stimuli. However, the N1 component elicited by 3.2° and 6.4° was not significantly different. Subsequently, a more positive event-related potential deflection during 3.2°(M= 5.251?V, SE=0.864) and 6.4°(M= 4.389?V, SE=0.720) than during the 9.6°(M= 2.758?V, SE=0.728) in the 350- 400 ms time window. Moreover, 3.2° elicited a more positive event-related potential deflection (P3) than did 6.4°during the same interval. It is obvious that the ERPs amplitude of N1 and P3 components evoked by target stimuli increased with the reduction of visual angle, which provides the similar model of the behavioral data (e.g., RTs). The N1component is related to the discrimination of the target stimuli appeared at the attended area, and the amplitude P3 component is suggested to reflect mental resource allocation during the processing of stimulus (e.g., larger amplitude is related to greater allocation of resources). Therefore, this study observed a clear ERPs effect under the case of non-cue of the spatial information of the target stimuli, most likely reflects the allocation of attention on the spatial scale adopted the means of selective pattern automatically.