Sex preferences for children are contingent on institutional and economic contexts, including family system. While the patrilineal joint family system of the Han Chinese tends to devalue daughters, the family systems of many of China's southern minorities are conducive to female autonomy and more equal sex preferences. The Li of Hainan Island provide an example. We examined household registers and surveyed women in a relatively isolated highland township inhabited by the Meifu, a Li sub-group. The Meifu depend largely on swidden agriculture, permit considerable sexual freedom to adolescent females, and, as expected, have more equal sex ratios among their children than other Hainan populations. There was a tendency for a preference for males in the one hamlet in the community with an exceptional endowment of irrigated land, suggesting that sex preferences are sensitive to local economic circumstances.