AbstractSilicon isotope separation from hexafluorodisilane (Si2F6) has been examined using a CO2 pulsed laser. Si2F6 containing certain isotopes was preferentially decomposed to SiF4 depending on the wavenumber (k) of the laser. 29Si and 30Si were concentrated in the SiF4 produced at k=945–955 cm−1, and in the residual Si2F6 at k=970–980 cm−1. The SiF4 containing 30Si of about 43.3% and 29Si at a maximum of 12.3% was continuously produced with a yield of 4.4% at k=951.203 cm−1 and 9.6% at 956.205 cm−1, respectively. The decomposition reaction of Si2F6 by the infrared laser irradiation could be explained as Si2F6(gas)+nhν→SiF4(gas)+SiF2(solid), calculated from a mass balance analysis of the experimental results. A 30Si concentration higher than 90% was estimated to be achievable by repeating the irradiation of the residual Si2F6 at around k=975 cm−1 and finally decomposing the Si2F6 to SiF4 at k=951.203 cm−1. SiC enriched with 29Si and 30Si was predicted to show an excellent low activation behavior in fusion neutron environments.