Temporal connectives play a crucial role in marking the sequence of events during language comprehension. Although existing studies have shown that sentence comprehension can be modulated by temporal connectives, they have mainly focused on languages with grammatical tense such as English. It thus remains unclear how temporal information is processed in tenseless languages. The present study used event-related potentials (ERPs) to examine how world knowledge is retrieved and integrated in sentences linked by zhiqian (before) and zhihou (after) in Mandarin Chinese (e.g., After/Before going to the countryside, Grandpa went to the city because the air there was fresh and pure). The critical words (e.g., fresh) were either congruent or incongruent with world knowledge. Relative to the after-congruent sentences, the after-incongruent sentences evoked a P600 on critical words and a negativity on sentence-final words, whereas relative to before-congruent sentences, before-incongruent sentences showed no significant difference on critical words but a sustained negativity on sentence-final words. Additionally, before-congruent sentences elicited a larger sustained positivity (P600) than after-congruent sentences. The results suggest that before is more difficult to process than after in Mandarin Chinese, supporting the iconicity account of temporal relations.