Information about the influence of basic density and lignin content on the propensity of wood to checks, simulated in a cleavage mechanical test, is scarce in the literature. Therefore, the objective of this research was to investigate the functional relationships between the cleavage strength and the basic density and lignin content of the wood. For this, two Eucalyptus grandis trees were felled at 22 years of age and specimens for the cleavage test were made. From these specimens, the basic density and lignin content were determined. The basal logs were sawn for making 45 specimens, 22 from the tree “A” and 23 from the tree “B”. The production of the specimens followed the suggestions of the ASTM D143 standard (ASTM 2014), being free from any defects that could mask the test results, without distinction of heartwood and sapwood or juvenile and mature wood. The mechanical test was carried out with aid of a universal testing machine EMIC, model DL 30000. The 45 specimens tested in the cleavage test were used to determine the basic density, as described in standard NBR 11941-02 (ABNT, 2003). After determining the basic density of the 45 specimens, 20 of them, 9 from the “A” tree and 11 from the “B” tree, were randomly selected for chemical analysis and determination of the lignin content in the wood. The extractives were removed according to the ABCP M3/89 standard (ABCP, 1974). The insoluble lignin content (Klason lignin) was obtained following the methodology described by Gomide and Demuner (1986). The samples were analyzed in duplicate. The lignin content soluble in sulfuric acid was determined following the methodology proposed by Goldschimidt (1971). The total lignin content was the result of the sum of the soluble and insoluble lignin content.