Resumo. The study objective was to evaluate the effects of light intensities upon the initial development of Leucaena leucocephala seedlings. The study was conducted inside a preservation area around a drinking water well used to supply Marechal Cândido Rondon residents from September 11th to November 20th, 2007. The seeds collected from mature leucaena trees located on an adjacent county (Toledo) went through break dormancy in vases, in water at 80 Celsius degrees and sown by using 10 units per vase. The vases were distributed in the area obeying an entirely randomized design with 13 light intensities (treatments) and 10 replications (vases), adding up to 130 vases. Five and two seedlings per vase were left after thinning executed 10 and 20 days after the sowing, respectively. Sixty days after the sowing, the seedlings were collected for the measurements of the stem diameter, the plant height, the number and area of leaves as well as the root, the stem and the leaf biomasses. Results indicated that there is a polynomial relationship of the fourth order between biometric parameters and light intensity; the highest significances were calculated for intensities of 643 and 2273 Lux indicating that leucaena can be considered pioneering and tolerant to direct sunlight.