PURPOSE: To obtain a diesel fuel composition which contains a minor portion of a detergent, effectively removes deposits from a diesel fuel injecting tube and keeps the diesel fuel injecting tube clean, and to provide a method of removing deposits from the diesel fuel injecting tube using the diesel fuel composition.

CONSTITUTION: This diesel fuel composition comprises a major portion of a middle distillate fuel oil and a minor portion of a diesel fuel detergent which comprises 4-alkyl-2-morpholinone represented by formula I and a reaction product of an alkylphenoxypolyoxyalkylene amine represented by formula II. In formula I, R1 represents an alkyl radical having 1 to 10 carbon atoms. In formula II, R2 represents a hydrocarbyl radical having 4 to 30 carbon atoms; (x) is a value of 4 to 50; R3 represents a methyl radical or a mixture of hydrogen and methyl radicals.