The present invention provides a 4'-C-substituted-2-haloadenosine derivative represented by the following formula [I], [II], or [III]: ##STR00001## (wherein X represents a halogen atom, R.sup.1 represents an ethynyl group or a cyano group, and R.sup.2 represents hydrogen, a phosphate residue, or a phosphate derivative residue). The present invention also provides a pharmaceutical composition containing the derivative and a pharmaceutically acceptable carrier therefor. Such derivative is useful as medicine for the treatment of Acquired Immune Deficiency Syndrome (AIDS).