In this study, the determination of density, porosity and permeability rates of sunflower silage at different stages of maturity and under different conditions of compaction was aimed. Whole-plant sunflower (Helianthus annuus L.) was harvested at three different maturity stages; (BA, Beginning of Anthesis (78%), ML, one-third Milk Line (70%) and BL, Black Line (64%)). Five compaction levels were done during ensiling. These were control (no compaction), vacuum and compaction with 150 kPa (C,), 248 kPa (C) and 498 kPa (C,). The chopped forages were ensiled in PVC (5.7 L) mini-silos. For porosity measurements, a tube system was designed, which operated according to ideal gas law. Permeability was measured to be the time during, which 1 L water passed through the silo container. The results of this study showed that the values of porosity, permeability and density were found to be significantly affected by the applications of compaction and stages of maturity.