Understanding the sequence (i.e. word order) of linguistic input plays an important role in sentence comprehension, particularly in languages such as English (Bornkessel-Schlesewsky et al., 2015). Neuroimaging and clinical research shows that left posterior superior temporal sulcus (pSTS) contributes towards sequence processing in both linguistic and non-linguistic contexts (Bornkessel et al., 2005; Wilson et al., 2010). To test the causal contribution of left pSTS for sequence-dependent sentence processing, we applied image-guided low-frequency repetitive transcranial magnetic stimulation (1 Hz for 15 minutes at 90% resting motor threshold) to this region in 23 healthy native English speakers. Participants undertook an auditory sentence processing task and were asked to identify the sentential actor or undergoer. Sentences were either semantically plausible or were rendered implausible by an animacy violation (e.g. “The student will write the answer” versus “The answer will write the student”). After sham-rTMS (control condition), participants predominantly selected the first noun as the actor and second noun as the undergoer, relying strongly on sequence cues (word order) for interpretation as expected in English speakers. By contrast, after real-rTMS, participants were more likely to use animacy as a cue to interpretation, with higher selections of the animate noun as the actor and inanimate noun as the undergoer regardless of word order. This effect also interacted with question focus and response time. These results indicate that sequence-based language processing is reduced after low-frequency rTMS to pSTS, suggesting a role for pSTS in processing sequential aspects of language such as word order.