Bio-based polymer composites are important key elements for development of sustainable future materials. Development of bio-based polymer composites is in the line of EU Green Deal policy. To achieve the United Nations sustainable Development goals it is neccessary to design new composite materials with possibly high content of renewable feedstocks being competitive with existing fossil based composite materials used for dedicated applications. Polyhydroxybutyrate-co-hydroxyvaleriate (PHBV) is convenient matrix material for achieving these sustainability goals because the polymer may be commercially synthesized by various microbial cell cultures. Modification of PHBV with rapeseed straw (RS) is convenient because this allows valorization of this low-cost agricultural residue. In spite of certain efforts in development of PHBV composites modified with various biomass residues (e.g. peach palm particles [1], wheat straw, brewers spent grains, olive mills [2] etc), there is lack of summarized scientifically grouned information on the property change of such composites throughout it life cycle starting from preparation of such composites and ending with it biodegradation. Consequently, the current research is focused on the development of PHBV composites with renewable feedstock microfibers, obtained from locally abundant low-cost agricultural residue biomass – rapeseed straw (RS). To increase interaction with PHBV matrix, the obtained RS microfibers were treated with Nmethylmorpholine N-oxide (NMMO), as a green alternative solvent in comparison to sodium hydroxide, typically used to improve properties of natural fibers. The content of RS in the PHBV composites has been changed from 0 to 10 wt.%. Triethyl citrate (TEC) has been used as plasticizer to reduce brittleness of the developed composites. The concentration of TEC was 20%, determined to be optimal according to our previous research [3]. PHBV/TEC/RS composites have been obtained by melt compounding approach. During the research the change of certain physical properties of the developed PHBV/TEC/RS composites has been investigated as a function of accelerated ageing exposure time and biodegradation time. Main results of the research demonstrate that -NMMO and alkali treatment of RS allows to obtain plasticized PHBV composites with improved biodegradability, increased stiffness but decreased strength and elongation, -accelerated weathering, leads to increment of stiffness, but reduction of tensile strength and elongation at break of the investigated PHBV biocomposites because of increased crystallinity of the biopolymer matrix, especially in the presence of RS, -all the developed PHBV composites demonstrate faster biodegradation in comparison to neat PHBV matrix, -surface treatment of RS microfibers delayed biodegradation of the developed PHBV composites