The objective of this work was to verify the influence of harvest time of jaraguá grass (Hyparrhenia rufa (Ness) Stapf) seeds upon their longevity under ambiental conditions of storage. After harvest, seeds were dryed under shadow to 10 to 11% of moisture, packed in cotton bags and stored. Periodícaly, at 0, 4, 8, 12 and 16 months, they were submited to the following determinations: germination, % of pure live seed, emergence, first counting and yield of pure germinating seeds. The analysis of the data led to the following conclusions: a) jaraguá grass seeds were dormant irrespectively of harvest time; b) seed dormancy naturaly overcomes by the storage for eight and four months respectively for immature and mature seeds; e) the seeds that showed longer longevity under ambientai conditions were harvested from 38 until 44 days after the initial head emergence.