Given the finite resources of seed production, a trade-off between seed weight and number was expected. However, it still remains unclear how the seed weight-number trade-off changes if there are some mechanisms to enhance resource acquirements during the fruit developments. Sinopodophyllum hexandrum presents furled leaves in flowering time but unfurled leaves in fruiting time, which is considered to enhance the photosynthates to fruit development. To determine the relationship between seed weight and number of S. hexandrum, we examined the altitudinal variations and the relationship between seed weight and number in the fruits from 27 populations of in 2009 and 2010. Our results showed that, along the altitudinal gradient, seed weight decreased significantly but seed number increased insignificantly, indicating that the selective pressure on seed production might come from seed dispersal in high altitude populations. There was no significant relationship between seed weight and number in most populations, but an inverse relationship was found between seed weight and number when the data from all populations were pooled, indicating the seed weight-number trade-off and resource limitation of seed production in S. hexandrum on species level. We suggested that the two unfurled leaves of S. hexandrum might contribute to the resources allocated to the fruit development via enhancing photosynthates, which might mask the seed weight-number trade-off on population level to some degree.