An environmentally friendly polymerization catalyst for polyalkylene terephthalate which does not use a heavy metal such as antimony, and a method for producing polyalkylene terephthalate using the catalyst. The catalyst for polymerizing a polyalkylene terephthalate is a titanium oxide sol containing an organic solvent as a dispersion medium, the sol has a light transmittance of not less than 50%, the light transmittance being measured by adjusting a concentration of the titanium oxide in the sol to 0.7 g/L and setting an optical path length to 1 cm in a wavelength range of 400 to 800 nm, and the amount of hydroxyl groups per 1 g of titanium oxide is not less than 1.8 mmol.