Lignocellulosic fibres obtained by dry grinding of three different solid agro-residues, i.e. wheat straw, brewing spent grains and olive mills, were compared regarding their potential use as fillers in poly(3-hydroxybutyrate-co-valerate) (PHBV) for food packaging applications. Differences found in their composition might have influenced their grinding ability, as observed with the difference of sizes, i.e. 109 !m, 148 !m and 46 !m, respectively. Thereafter, composites structure was characterized regarding their morphology, fibre/matrix interaction, matrix molecular weight and crystallization behaviour. Poor fibre/matrix adhesion, degradation of PHBV polymer chains, and decrease of PHBV’s crystallinity were evidence. Consequently, mechanical properties were degraded in presence of the fibres. Water vapour transfer rate of composites was increased with wheat straw fibres introduction while it was decreased for olive mills-based materials. Regarding the food packaging applications, PHBV/wheat straw fibres composites appeared as promising materials to reach the requirements of respiring food products, whereas PHBV/olive mills composites would be more adapted for water sensitive products. ; This work was also supported by FEDER funds through the program COMPETE (project PTDC/AGR-ALI/122741/2010), by the Portuguese Foundation for Science and Technology (PEst- C/CTM/LA0025/2013 – Projecto Estratégico – LA 25 – 2013–2014 – Strategic Project – LA 25 – 2013–2014) and by Programa Operacional Regional do Norte (ON.2) through the project “Matepro – Optimizing Materials and Processes”, with reference NORTE-07- 0124-FEDER-000037 FEDER COMPETE