Observations were made on the development of sugar cane roots (var. Co. 290) in red soil ("terra-roxa-legitima") at the Usina Tamôio, Araraquara. Root samples were taken from commercial sugar cane fields when they were 6, 12 and 18 months old. The results showed that the distribution of the root system of the variety studied was uniform in the different layers of soil. Most roots were present in the upper 30cm of soil, with an average for the 3 samplings of 59.3%. Roots of 6-month old plants already reached 2.10m, and after 18 months they reached as far as 3.30m. The maximum amount of living roots was found when the plants were 12 months old, this being correlated with the highest growth rate of the plant. A sugar cane field that yields 100 tons per hectare was estimated to have about 1.8 tons of roots at 6 months and 8 tons of them after 18 months.