<p>Many studies found that structural priming in production relied on cognitive resources (e.g., working memory), suggesting a resource-constrained mechanism of syntactic processing. To investigate the mechanism of structural priming in comprehension (automatic vs. resource-constrained), we constructed two eye-tracking experiments to test the role of working memory (i.e., a number series recall task between prime and target exerting high or low working memory load) in structural priming during visual-world comprehension. The priming effect is evaluated by the proportion of looks to predicted referents for two critical time windows in target sentence processing: the target verb and the first syllable of the first postverbal noun. When prime and target involved different verbs (Experiment <InternalRef RefID="Sec2">1</InternalRef>), structural priming in both time windows was similar between the high- and low-load conditions. When prime and target involved same verbs (Experiment <InternalRef RefID="Sec12">2</InternalRef>), structural priming in the time window of the first syllable of the first noun phrase was weaker in the high-load than in the low-load condition. Within the time window of the first syllable of the first noun phrase, a lexical boost effect occurred in the low-load condition but not in the high-low condition. Overall, structural priming in comprehension is partially automatic, while lexically mediated structural priming is modulated by working memory, supporting the implicit learning theory.</p>