Rice varieties and seed management involve a complex system dealing with various problems such as variety adoption, agro-biodiversity conservation, and quality seed supply. A participatory modeling experiment on rainfed lowland rice variety and seed management in lower northeast Thailand has been launched to better understand the system and its problems. Conceptual modeling was done through inter-institutional research team meetings, stakeholder analysis, surveying of stratified randomly sampled farmers and seed supply agents in Ubon Ratchathani Province, and by conceiving and using role-playing games (RPGs) with stakeholders. The system to be analyzed was divided into three subsystems, i.e. farmers' decision making regarding the choice of rice varieties, farmers' management of rice seeds, and the seed supply sub-system. A first RPG focusing on the first two subsystems was used with 25 farmers in two different gaming sessions. Observations and findings from the RPG helped to validate and to improve the conceptual model prepared by the research team. It also builds a shared understanding of farmers' rice varieties and seed management. Limited access to information about varieties and seeds, the need for early maturing varieties, and the scarcity of quality seeds were identified as current constraints of the system. A second RPG representing the seed supply subsystem is being conceived. Later on, a multi-agent system model of the whole system will also be developed and used to simulate scenarios identified by stakeholders and to discuss their results to facilitate collective learning and improvement of the current situation.