This paper presents the design and construction of a Chinese opinion corpus. Based on the observation on the characteristics of opinion expression in Chinese online product reviews, which is quite different from in the formal texts such as news, an annotation framework is proposed to guide the construction of an opinion corpus based on online product reviews. The opinionated sentences are manually identified from the review text. Furthermore, for each comment in the opinionated sentences, its 13 describing elements are annotated including the expressions related to the target product attributes and user opinion expressions as well as the polarity and degree of the opinions. Currently, 12,724 comments are annotated in 10,935 sentences from product reviews. Through statistical observation on the opinion corpus, some interesting characteristics of Chinese opinion expression are presented. This corpus is helpful to support systematic research on Chinese opinion analysis.