[en] The MOX fuel has been fabricated by attrition milling in cooperation with PSI. Two MOX fuels are being loaded in IFA-651 with the reference MOX fuel provided by BNFL. The MOX fuels have been irradiated in Halden reactor from June of 2000 until now and the in-pile test will be continued up to ∼ 50 MWd/kgHM for ∼ 5 calendar years. One of KAERI's MOX fuel is instrumented with ET while each of the other two rods has TF at the top end. All rods have PF at the bottom end. In addition, one KAERI's MOX fuel is instrumented with EF at the top of the fuel stack. MOX fuels have been successfully irradiated during eight cycles (2000. 6 ∼ 2005. 10), of which results have been reported already. The irradiation tests until the fourth cycle (IFA-651.1) can be summarized as follows: The densification of the MOX fuel rods shows 1∼2%, which means the densification has not been influenced by different fabrication method. On the other hand, the densification estimated by EF measurement indicates very negligible, which is much lower than values from PF. There is a fission gas release of 1 ∼ 3% during the third cycle. The fission gas release behavior at the MOX fuels is comparable to that of UO₂ fuel. The swelling estimated from PF measurement is ∼ 0.850%/10MWd/kgHM. At the end of four cycle irradiation, the IMF-2 rod was taken out for PIE. The second irradiation test of IFA-651.2 up to the eighth cycle from February 2004 to October 2005 reached the burnup of more than 40MWd/kgHM. The fuel centerline temperature was up to 1200 .deg. C. The higher linear heating rate of 250 ∼ 300 W/cm was observed due to the removing of IMF-2 rod. The fission gas release was 16% and 27% for MOX-ATT-ET and MOX-ATT-TF, respectively. The COSMOS code analyzed the in-pile data of IFA-651.1 and 2. The temperature and rod internal pressure was well simulated with the effect of thermal recovery accompanying with the significant fission gas release. Based on the irradiation test up to now, the attrition milled MOX fuel rods have very comparable to SBR MOX fuel