Zirconium phosphate ethylphosphonates, Zr(O₃POH)_2−x(O₃PC₂H₅)_x (hereafter ZrP(PC₂)_x), with x = 0.6–1.6, were first synthesized from the mixtures of zirconyl propionate, phosphoric and phosphonic acids in THF, and then functionalized by reaction with 1,2-epoxydodecane, C₁₂H₂₄O, at 60 °C. Thermogravimetric analysis together with ³¹P NMR analysis proved that only the P–OH groups of ZrP(PC₂)_x quantitatively reacted with the epoxy functionality, leading to the formation of P–O–C bonds. The interlayer distance of the zirconium organophosphate ethylphosphonates, Zr(POC₁₂)_2−x(PC₂)_x, changes continuously from 27.2 Å (for x = 0.6 and 2 − x = 1.4) to 16.6 Å (for x = 1.4 and 2 − x = 0.6), indicating that the ethylphosphonate and organophosphate functionalities are randomly distributed on the layers. The sample with composition Zr(POC₁₂)_0.9(PC₂)_1.1 was used to prepare a polyethylene (PE) based composite containing 5 wt% of filler. Preliminary characterization of the composite was carried out by X-ray analysis, thermogravimetric and DSC measurements. A delay of the thermal decomposition of the polymer up to 40 °C and a shift of the polymer melting temperature toward lower values was observed in the presence of the filler, indicating that a significant polymer–filler interaction occurred when alkyl chains of different lengths are interdispersed on the layer surface.