Multiple repetitions of collocations in second language (L2) reading produce gains in collocational knowledge. However, it is less clear how typographic enhancement affects the learning of different types of L2 collocations through reading. The present experiment investigated contextual learning of English lexical (verb + noun) and grammatical (preposition + noun) collocations by Chinese speakers over two days. We manipulated the learning conditions by bolding or not bolding multiple instances of the target collocations in reading texts. A cued-recall (gapfill) post-test was used to measure collocational knowledge. We observed greater accuracy of responses with grammatical (but not lexical) collocations when the collocations were bolded than when they were not bolded. We argue that bolding likely made prep + noun collocations more perceptually salient to the learners during reading. We conclude that contextual learning of L2 grammatical collocations is likely to benefit from drawing explicit attention to the whole expressions in written input.