This paper examines the construction of sexual knowledge in contemporary China through a typical instance of its production--the marriage manual "Marital Medicine". China's reform era has seen rapid changes in attitudes to sex and in sexual conduct, and recent government interest in sex education has been motivated by a desire to halt the "negative impact" of modernization on marriage and the family. Education for legitimately sexually active adults has taken a number of different forms, but the diversity of media is not matched by diversity of content. Sexual knowledge speaks in an overwhelmingly uniform and universalizing voice, and is constructed around a nature narrative, which sets out how bodies are sexed, how bodies have sex, and the legitimate forms of their intimate relationships. This paper is an examination of the production (rather than consumption) of sexual knowledge, and shows the current boundaries of "normal", "natural" and "healthy" within which people understand and make choices about their sexual lives. (Contains 26 notes.)