Objective To further study the role of fibroblast growth factor 9 ( FGF9) in neurodevelopment by establishing a mouse model of conditional FGF9 knockout in oligodendrocytes. Methods Olig1-Cre transgenic mice were crossed with FGF9 transgenic mice ( FGF9^{flox / flox} ). Then, female FGF9^{flox / wt} / Olig1-Cre⁺ mice were mated with male FGF9^{flox / flox} mice to obtain oligodendrocyte-specific FGF9 knockout mice (FGF9^{flox / flox} / Olig1-Cre⁺ ) in the F3 generation. To confirm that FGF9 had been conditionally inactivated in the oligodendrocytes alone, genotyping using PCR, western blotting, and laser confocal were used to evaluate the expression of FGF9 mRNA and protein. An initial characterization of the phenotype of the conditional knockout (CKO) mice was then made. Results We confirmed that the expression of the FGF9 mRNA and protein were appropriate in the FGF9^{flox / flox} / Olig1-Cre⁺ mice. Preliminary phenotypic analysis showed that FGF9 CKO mice survived for the same period of time as control mice and were fertile but developed slowly. Conclusions We have successfully established mice with a CKO of FGF9 in oligodendrocytes, which causes growth retardation.