The invention relates to a process for FCC pretreatment by mild hydrocracking of a hydrocarbon feedstock that comprises a vacuum distillate fraction or a deasphalted oil or else a mixture of these two fractions, said primary feedstock, to produce gas oil and an effluent having an initial boiling point of more than 320.degree. C., said effluent (FCC feedstock) then being subjected to a catalytic cracking, process in which at least 85% by weight of said primary feedstock ends above 375.degree. C. and at least 95% by weight of said primary feedstock ends below 650.degree. C., whereby the mild hydrocracking is performed under an absolute pressure of 2 to 12 MPa and at a temperature of between 300 and 500.degree. C., characterized in that the hydrocarbon feedstock also comprises a lighter hydrocarbon fraction, a so-called secondary feedstock, of which at least 50% by weight ends below 375.degree. C. and at least 80% ends above 200.degree. C.