Poly(butylene succinate) (PBS) is a bio-based and biodegradable aliphatic polyester with good thermal and mechanical properties comparable to commodity plastics. The addition of cellulose filler reinforces the polymer matrix, thus, increasing mechanical, barrier and biodegradation properties. PBS/cellulose composites are versatile materials with potential applications in packaging, agricultural, automotive, and biomedical fields. The selection of cellulose filler from recycled cellulose to nanocellulose can be used to develop materials for specific applications. The majority of commercially used commodity plastics are non-biodegradable. Although, production of bio-based plastics and recycling alleviates some of the environmental issues these products still often end up in landfills or nature as permanent pollution. This work uses biobased PBS and cellulose from renewable circular resources to develop sustainable composite materials. The PBS/cellulose composites must fulfil demanding properties during materials application, while retaining high dimensional stability and mechanical properties. In addition, after the life cycle ends, it is expected that the composite will rapidly designate in the soil. This is achieved using a hydrophobic PBS matrix that offers excellent ductility and rigid cellulose particles with excellent reinforcement capabilities. Cellulose fillers have exceptional morphology that can be tailored by mechanical and chemical processing to a specific size, while surface chemistry can be adjusted with modification methods or compatibilizers. Cellulose is an excellent alternative to inorganic polymer fillers that are unsustainable and often mined in a harmful way to the environment. The results of the work are presented into four parts: Part 1 describes the development and investigation of PBS/recycled cellulose composites. The use of recycled cellulose from tetra pak was explored regarding including waste material into circular sustainable economy. Loading with cellulose filler up to 50 wt.% were explored, and tensile, thermomechanical, and thermal properties, including biodegradability and dimensional stability with immersion in water were tested for prepared composites. Part 2 describes the preparation and comparison of PBS composites with varied nanocellulose and microcellulose filler ratios. The use of freeze-drying process was applied for nanocellulose processing and simplified melt mixing of PBS/nanocellulose composite was proposed. Total filler loading was fixed at 40 wt.% to compare selected fillers extensively. The section demonstrates the advantages of micro-sized filler in the direct melt mixing process. Part 3 describes the in-depth research and optimization of PBS/nanocellulose composite preparation. The direct solvent casting is used as a reference, while the optimized process with masterbatch is proposed as an alternative. It was discovered that melt mixing significantly improved fillers ability to reinforce polymer’s matrix showing much higher tensile and thermomechanical properties. Part 4 describes the application of various modification, coating, and computerization methods for improving mechanical and thermal properties for PBS/microcellulose composites. Exceptionally high loading 70 wt.% of cellulose was used to achieve high sustainability of composite materials and test selected preparation routes. The Doctoral Theses has been written in English; it consists of 135 pages, 58 figures, 18 tables and 308 reference sources.