The present invention relates to a pharmaceutical composition for treatment of cancers containing Sindbis virus as an active ingredient, a method for treatment of cancers, which comprises administering a therapeutically effective amount of Sindbis virus to a mammal having cancers, a method for identifying cancers, which includes introducing Sindbis virus into an animal, thereby detecting a Sindbis virus protein or Sindbis virus RNA in vital tissues of the above animal, a method of identifying cancers, which includes introducing into an animal Sindbis virus having a reporter gene incorporated therein, thereby, detecting the product of the reporter gene in vital tissues of the animal, and a method of identifying cancers, which includes detecting a increase in antibody titer to the Sindbis virus protein or the product of the reporter gene in the aforementioned animals.