This aim of this article is to analyze the relation of size and operational efficiency of sugar and ethanol plants in the northeastern region of São Paulo state. In order to achieve this goal, a survey was conducted to identify the consumption of the main resources (inputs) and product creation (outputs) in a random sample of twenty six units, which allowed for their classification according to size. This enabled the creation of an efficiency ranking, using Data Envelopment Analysis (DEA), whose variables were chosen by the stepwise method. The results suggest that, for the plants studied, there is no direct relation between size and operational efficiency, which can be explained by technical aspects associated to the inputs. The results provide subsides to the managers in the sugar and ethanol plants, who can then better structure their operational strategies.