The change on the harvesting sugar cane operation from the manual to mechanized cut  increased the amount of sugar cane cut by the mill per day, but the operation increased the cane loss, which is left behind on the field. The purpose of this work was to contrast the accuracy achieved by an auto guidance system on the passes of a sugar cane harvest machine over the field, which was planted by a tractor guided by the system too, contrast the quality of the harvested product (mineral and vegetal impurities) and cane loss, when compared to the manual guidance method. The field test was conducted with two treatments: auto guidance and manual guidance; during two period of time: day and night; and four blocs per treatment: pass/row 1 to 4. Each GPS position recorded represented a single sample, which was used to calculate the error pass when compared with the planned pass. The statistical analysis was made with SISVAR software, calculating the Tukey test at 5% of significance. It was concluded that the use of the auto guidance system does not increase the machine operational efficiency on the mechanized sugar cane harvest operation, once its efficiency is guided by the sugar cane wagon. The mineral and vegetal impurities were the same for manual and auto guidance systems, likewise the sugar cane field loss. The use of auto guidance systems decreased the error of the machine over the planned row track.