Abstract: The present invention relates to a novel thermoplastic composition, characterized in that it contains: a) 15% to 60% of at least one starchy material; b) 10% to 30% of at least one starchy material plasticizer; c) 15% to 70% of at least one polyolefin; and d) 10% to 40% of at least one plant material selected among plant fibers and plant fillers. The invention also relates to a thermoplastic composition preparation method that includes the following steps: (i) selecting at least one composition (a) containing at least one starchy material, one plasticizer of said starchy material, and one polyolefin; (ii) selecting at least one plant material (b) selected among plant fibers and plant fillers, said plant material being formed of particles, the dimensions of which are between 0.5 and 5000 micrometers; and (iii) mixing the composition (a) and the plant material (b) so as to obtain the thermoplastic composition according to the invention.