We experimentally demonstrate an ultrafast mode-locker based on a CoSb3 skutterudite topological insulator for femtosecond mode-locking of a fiber laser. The mode-locker was implemented on a side-polished fiber platform by depositing a CoSb3/PVA composite. The measured modulation depth and saturation power for the transverse-electric mode input were ～5% and ～8.7W, respectively, and ～2.8% and ～10.6W for the transverse-magnetic mode input. By incorporating this mode-locker into an erbium-doped fiber-based ring cavity, we were able to readily generate mode-locked, soliton pulses having a pulse width of ～833fs at 1557.9 nm. The 3-dB bandwidth of the output pulses and time-bandwidth product were ～3.44 and 0.353 nm, respectively. To the best of the authors’ knowledge, this is the first demonstration of the use of a skutterudite-based saturable absorber for femtosecond mode-locked pulse generation.