This article uses a CGE model to analyze the impacts on households' food security of the poor of possible trends of agricultural productivity in Burkina Faso. Negative trends are the result of land degradation while public investment in agriculture, through the provision of public goods, is expected to induce the positive trend. The results show not only the high sensitivity of consumption levels of the poor to the level of agricultural productivity but also stronger impacts on the urban poor. While the current food situation is already characterized by severe food insecurity, a decline in agricultural productivity is likely to plunge the urban poor into a food crisis. By contrast, positive trend on agricultural productivity is effective in the fight against poverty and food insecurity. Changes of agricultural productivity influence food consumption of the poor mainly through a strong variation in agricultural prices and real incomes.