As to invasion of the human respiratory tracts by trichomonads, few cases have been reported in the world; so far as is known, only one case has been available in Japan. To have more information on the infection, such a case report seems to be important. A 70-year-old male from a nearby village presented to the National Hospital, Kochi City. The patient was hospitalized as the result of hemoptysis associated with shortness of breath, wheezing and fever with severe chest pain. Chest x-rays showed a high retention of the pleural effusion. Trichomonas tenax was observed in the effusion and found to be concomitant infection with Escherichia coli, maybe a main causative agent of the disease in this case. The protozoan measured an average size of 12.44 ± 1.60 (9.09–16.16) µ in length and 8.52 ± 2.41 (4.04–12.2) µ in width (n = 30).