This paper contributes to the gender-and-marketplace literature by exploring whether and how the ongoing, under-researched food-to-cash crop transformation of rice in Tanzania reinforces or challenges the "doing of gender". We apply Acker's "doing gender" framework, where gender is done by following normative conceptions and undone by challenging them. We analyze women and men's everyday practices and relations in terms of identities, divisions, symbols and interactions. The empirical material includes observations, in-depth interviews and focus group discussions with women and men traders, farmers and key informants at two rice markets in Kyela, south-western Tanzania. We find that this transformation of rice has resulted in more processes of doing than undoing gender. Too, more women than men undo gender. Since men and masculinity are constructed as superior to women and femininity, this makes it more difficult for men to undo gender. The structures of the marketplaces also seem to influence these processes. Surprisingly, the old marketplace offers more avenues to undo gender, whereas the new, government-initiated marketplace reinforces the doing of gender.