The present invention provides a process for preparing 4-methyl-5-nonanone of the following formula (3), the process comprising at least a step of subjecting pentanoic anhydride of the following formula (1) and a 2-pentyl nucleophilic reagent of the following general formula (2), in which M represents Li, MgZ1, or ZnZ1, wherein Z1 represents a halogen atom or a 2-pentyl group, to a nucleophilic substitution reaction to produce 4-methyl-5-nonanone (3), as well as a process for preparing 4-methyl-5-nonanol of the following formula (7), the process comprising at least steps of preparing 4-methyl-5-nonanone and subjecting the obtained 4-methyl-5-nonanone and a reducing agent to a reduction reaction to produce 4-methyl-5-nonanol (7).