Due to its high positive Seebeck coefficient (125 mu V K-1) and low electrical resistivity (10-40 m Omega cm) Ca3Co4O9 is a material of interest for thermoelectric power generator-based metal-oxide thin films. In the present work, we emphasize the tremendous role of ex-situ thermal treatment on the structural, electrical and low temperature thermoelectric properties of PLD grown Ca3Co4O9 thin films. We evidence a crystallization of the Ca3Co4O9 misfit layer between 873 K and 923 K, allowing a tailoring of the thermoelectric properties of Ca3Co4O9. A high maximum power factor of 2 x 10(-4) WM-1 K-2 at room temperature is attained for the most performing films.