How dialectal lexis may interfere with Putonghua spoken in a region has long been talked about but has rarely received much attention in scholarly literature. The issue is often complicated by the fact that there is a lack of a set of commonly recognized criteria with which to define regional Putonghua varieties vis-à-vis the regional dialects. Against this background, I have in this paper first argued for taking Putonghua education and use at, after and beyond school as the bench mark for defining regional Putonghua varieties either as true linguistic entities or as conceptual entities. Then, I have examined how question words and interrogative particles in the Chengdu dialect find their way into the Putonghua spoken in that region, attributing the lexical interference to two main factors. The first is the salient linguistic connection between Putonghua and the Chengdu dialect, which is a major southwestern branch of Mandarin, and the second is more sociolinguistically related, being associated with the speaker’s education and need for using Putonghua at work against a rapidly developing regional economy.