To obtain the subject composition capable of suppressing the amount of intake valve deposits in a spark-ignition internal combustion engine and minimizing the degree of the valve sticking by including a fuel for the spark- ignition internal combustion engine, a Mannich detergent and a specific polybutene.

This fuel composition contains (A) a spark-ignition fuel (preferably containing a gasoline), (B) a Mannich detergent (preferably containing a reactoinal product of an alkyl-substituted hydroxy-aromatic compound with an aldehyde and an amine) and (C) a polybutene manifesting <1.4 molecular weight distribution (preferably a highly reactive polybutene having 500-2,000 number-average molecular weight). The amount of intake valve deposits in a spark-ignition internal combustion engine can be minimized or reduced to perform the operation by feeding the fuel composition. An additive concentrate is prepared by including the components C and B and a diluent so as to provide (0.1:1) to (1:1) ratio (weight ratio) of the components C:B.