The invention provides a bitumen composition comprising a bitumen and a modified clay which clay is obtainable by subjecting a clay having a layered structure to a treatment with a compound that is selected from the group consisting of onium compounds having the general formulae (R1R2R3R4X)+ or (R1R2Y)+, wherein X represents N or P, Y represents S, and wherein at least one of R1-R4 represents an aromatic hydrocarbon substituent, a hydroxyl or amino functionalized aliphatic hydrocarbon substituent or a poly(ethyleneoxide) substituent. The invention further provides a process for preparing said bitumen, an asphalt composition comprising aggregate and said bitumen composition, and the use of said bitumen composition in an asphalt composition for road applications.