An efficient one-pot synthesis of benzimidazole derivatives by the condensation between various o-phenylenediamine and substituted aromatic aldehyde using ZnFe2O4 as a nano-catalyst under ultrasonic irradiation conditions was described. Remarkable advantages of the present synthetic strategy over the previously reported methods are shorter reaction times, higher isolated yields and simple work-up procedure. The presence of electron withdrawing and electron donating groups on the aromatic rings did not affect the yield of the product. The ZnFe2O4 catalyst was recycled after completion of reaction and was reused.