This work was carried out at the Seed Analysis Laboratory of the Plant Production Department of São Paulo State University (UNESP), Botucatu-SP, aiming to evaluate the cyanide (KCN) effects on Brachiaria plantaginea (Link.) Hitchc. seed overcoming dormancy. Seeds with total (absence of glummes) and partial scarification (prescence of scratched glummes) were placed to germinate in gerbox type boxes on two layers of blotting paper imbibed with 12ml KCN solutions of 0.0; 3.1; 4.6; 6.1; 7.7; 9.2; 10.7; 12.4; 13.9 and 15.3mmol.l-1, at 25oC. The germination evaluations were made after four, seven and 14 days. The results showed that 3.1mmol.l-1 KCN, promoted a 30% increase in B. plantaginea seeds radicle emergence, with either presence or absence of glummes. This remained constant up to 6.1mmol.l-1, after wich the radicle emergence decreased up to 80% in relation to the control. In spite of that, high concentrations, over 9.2mmol.l-1, improved seedling development.