The objective of this paper is to present a methodology for assessing the environmental sustainability of milk-producing farms, which consists of a set of spreadsheets (MS-Excel platform) comprising nine parameters (waste disposal, water sources, environmentally protected area, legal reserve, use of pesticides and fertilizers, property slope gradient, erosion, forest fires and land uses) sub-divided into 13 sub-parameters. From these indicators, weighing matrices were constructed with sub-parameters, in which quantitative data obtained in field and laboratory were transformed into impact indices, numerically expressed. This proposal was developed and applied as a pilot project on four dairy farms in the municipality of Arroio do Meio/RS/BRAZIL, where field diagnosis, map use and land cover designs and the construction of an environmental sustainability index were carried out. The environmental assessment allows the producer/administrator to determine which attributes of the activity may be inconsistent with sustainability and the decision-maker to have an indication of measures to promote or control the activities according to local development plans; moreover, it provides an objective unit to measure the impact so as to assist in the qualification and certification of agricultural activities.