In almost all types of vegetation there are species that can cause toxicity to livestock that consumes. The poisoning caused problems in many different animals can affect reproduction, weight gain, and even death. These problems are causing economic losses in the livestock industry it is necessary to quantify but very difficult to achieve it. In Sonora, has been diagnosed rangeland of overgrazing, which manifests itself in a deterioration that diminishes the species desirable and undesirable increases, among these plants are toxic. We have identified 184 species that are toxic and within them there are 59 species that consume livestock and cause problems. For the foregoing are raised by this study, in order to try to estimate the economic impact that cause toxic plants on livestock productivity in Sonora. We used various sources of information for developing analysis and calculations that may come closer to quantifying the economic effects. We used the methodology described by Nielsen et al. (1990) for estimating these losses. The results show that a conservative estimate of the economic effect of these plants on sonorense livestock may represent a loss of around 90 million pesos a year.