This study aimed to investigate the timecourse and neural underpinnings of the coding of radical positions in Chinese character reading. To isolate effects of radical positions, four types of pseudocharacters were created in which the constituent radicals appeared in positions varying in probability of occurrence, that is, Unique, Dominant, Subordinate, or Illegal positions. Twenty native Chinese readers performed a character detection task where real characters were identified among pseudocharacters. The event-related potential data demonstrated that Illegal items were reliably distinguished from other pseudocharacter items within 100 ms, with larger P100 amplitudes at left posterior electrodes. At the N170, Illegal items elicited a smaller negativity than Unique items. In these time windows, pseudocharacter conditions in legal radical positions did not differ among themselves. The early timecourse effects suggested that radical position legality was detected at the initial stage of visual processing, which challenged theoretical models that assume primacy of position-general radical representations.