An object of the present invention is to provide a process for producing a modified conjugated diene-based polymer suitable for preparing a polymer composition excellent in the fuel cost saving effect. The present invention provides a process for producing a modified conjugated diene-based polymer, comprising reacting a conjugated diene-based polymer having a monomer unit based on a conjugated diene compound and a monomer unit based on a compound represented by the following formula (1), with an organometallic compound, and reacting the resulting reaction product with a hydrocarbyloxysilane compound: wherein R11, R12, R13, R14 and R15 each represent a hydrogen atom or an alkyl group, at least one of R11, R12, R13, R14 and R15 is an alkyl group, R16, R17 and R18 each represent a hydrogen atom or a hydrocarbyl group, R19 represents a hydrocarbylene group, and k represents 0 or 1.