In two eye-tracking studies we investigated the influence of Mandarin numeral classifiers - a grammatical category in the language - on online overt attention. Mandarin speakers were presented with simple sentences through headphones while their eye-movements to objects presented on a computer screen were monitored. The crucial question is what participants look at while listening to a pre-specified target noun. If classifier categories influence Mandarin speakers' general conceptual processing, then on hearing the target noun they should look at objects that are members of the same classifier category - even when the classifier is not explicitly present (cf. Huettig & Altmann, 2005). The data show that when participants heard a classifier (e.g., ba3, Experiment 1) they shifted overt attention significantly more to classifier-match objects (e.g., chair) than to distractor objects. But when the classifier was not explicitly presented in speech, overt attention to classifier-match objects and distractor objects did not differ (Experiment 2). This suggests that although classifier distinctions do influence eye-gaze behavior, they do so only during linguistic processing of that distinction and not in moment-to-moment general conceptual processing.