He said a 47-year-old Thai man who had engaged in physical contact with a foreigner was admitted to Vajira Hospital last week after developing fever, muscle pain and rash throughout his body.
He said the hospital's medical staff would be monitoring the patient's symptoms for 21 days.
Meanwhile, Department of Disease Control director-general Opas Karnkawinpong said they are conducting tests on 10 people who had come in contact with the second monkeypox patient.
He added that the disease investigation team is accelerating tracking down other people who came into contact with the patient.
He also advised people who develop monkeypox symptoms to consult a doctor at hospitals near their homes.