This paper explored pluralistic ignorance in the context of disputes between Hong Kongers and mainland Chinese in Hong Kong. It examined whether people could properly observe the public opinion of a collective to which they did not belong. Using two representative samples of mainland Chinese students and local students from three Hong Kong universities, this paper found that mainland students overrated the local public’s unfavorability concerning Chinese mainlanders and the Chinese government. This overestimation appeared positively linked to their attention to media content on the Sino–Hong Kong relationship and the degree to which they observed the relevant media content to be partial toward Hong Kong yet negatively related with their interpersonal communications with Hong Kongers about matters concerning the Sino–Hong Kong relationship. The overrating of the local public’s unfavorability of Chinese mainlanders and the Chinese government decreased the alacrity of mainland students to stay in Hong Kong for further study, employment, or domicile. Based on the results of this inquiry, further research on pluralistic ignorance is advised in order to establish how migrants discern the mainstream opinion in the society to which they move.