Theory of mind (ToM) has been known as one of the main developmental deficits in individuals with autistic spectrum disorders (ASDs). It is therefore both theoretically and practically important to observe how the two concepts correlate with each other in individuals with ASDs. The current study aimed to longitudinally investigate this issue in Mandarin-speaking children and adolescents with ASDs. Forty-two children and adolescents were followed for about a year and tested at two time points approximately a year apart. Theory of mind scores at time 1 and time 2 were measured with both verbal and non-verbal ToM tasks. Comprehension of sentential complements (SC) was also tested at the two time points with cognition (“think”) and communication (“say”) verbs of both true and false complementation. Our findings show that SC at time 1 can successfully predict ToM at time 2 while controlling for chronological age, general language production abilities and ToM at time 1. However, ToM at time 1 cannot successfully predict SC at time 2 given the same controlled conditions. Thus, the results suggest that the comprehension of sentential complements should play a causal role in ToM development in Mandarin-speaking children and adolescents with ASD. However, our findings regarding how each of the fourtypes of SC independently contributes to ToM abilities a year later are not totally consistent with past research done with English-speaking participants. Some possible reasons for the differences have been discussed. Suggestions for future studies have also been proposed.