We report the investigation of boron substitution on structural, electrical, thermal, and thermoelectric properties of Ca-3_xBxCo4O9 (x=0, 0.5, 0.75, and 1) in the temperature range between 300 K and 5 K. X-ray diffraction studies show that the Ca3Co4O9 phase is successfully preserved as the majority phase in the x=0.5 sample despite the small size of boron ions. Electrical transport measurements confirm that B3+ substitution for Ca2+ causes an increase in resistivity due to the decrease in carrier concentration. x=0.5 sample is found to have a Seebeck coefficient of 181 mu V/K at room temperature which is similar to 1.5 times higher than that of the pure Ca3Co4O9. Our results indicate that the chemical pressure due to the large ionic radii difference between B3+ (0.27 angstrom) and Ca2+ (1 angstrom) enhances the thermoelectric properties as long as the unique crystal structure of Ca3Co4O9 is preserved. (c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.