Polyvinyl chloride/wood flour (WF)/organoclay (OMMT) ternary composites were prepared by melt blending. Chemically treated and untreated pine WF were used as filler, and organically modified montmorillonite or OMMT was added in order to get a potential synergy effect between polyvinyl chloride, untreated wood flour (UWF), or chemically treated WF. The OMMT loading in the composites was 0.5, 1, or 1.5 wt%. The chemically treated and UWF loadings were 1, 5, and 10 wt%. The composite specimens were subjected to mechanical tests (evaluation of tensile strength, elongation at break, and Shore A hardness), thermal stability (Beilstein test), processability characterizations, water resistance absorption, and morphological (optical microscopy) observations. The main results showed that the chemically treated WF were more efficient than the UWF for improving the mechanical and physical properties of polyvinyl chloride. Similar results were reported in the scientific literature. Therefore the chemically treated WF can be a cheap, eco-friendly, and renewable substitute for chalk as a filler which is normally used in the fabrication of Polyvinylchloride based cable insulators.