The continuous increase of synthetic plastics in the environment creates an urgent need for new, biodegradable materials. Polyhydroxyalkanoates (PHA) have recently emerged as promising candidates, especially poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). PHBV is a biodegradable polymer with good mechanical properties and great potential to replace traditional fossil fuel-based plastics. However, its high market price limits its wider application. This work focuses on the preparation of biomaterials based on PHBV and thermoplastic starch (TPS). TPS was prepared using the casting method with glycerol as a plasticizer. TPS and PHBV blends were prepared in a Brabender kneader, and their morphological, thermal, mechanical, and barrier properties were analyzed. Differential scanning calorimetry (DSC) was used to determine phase transitions, while thermogravimetric analysis (TGA) was conducted to gain insight into the thermal stability of the materials. Basic mechanical properties, tensile strength, and elongation at break were tested using a mechanical testing machine. Morphology was examined using a scanning electron microscope (SEM), and water vapor permeability was determined using the Herfeld method. DSC analysis indicates partial miscibility of TPS/PHBV polymer blends, as evidenced by the shift in the glass transition temperature of each component. TGA analysis confirmed that all TPS/PHBV polymer blends decompose in two stages: the first stage corresponds to the decomposition of the thermally less stable PHBV, while the second stage involves the decomposition of the thermally more stable TPS. Mechanical tests showed that the tensile strength values of TPS/PHBV polymer blends fall between those of the pure components TPS and PHBV. The water vapor permeability values of TPS/PHBV polymer blends also fall between the water vapor permeability values measured for the pure components. SEM analysis further confirmed the partial miscibility of TPS/PHBV polymer blends.