We report detection of four IRAC sources in the GOODS-South field with an extremely red color of H - [ 3.6 ] > 4.5 .
The four sources are not detected in the deep HST WFC3 H-band image with H _ { limit } =28.3 mag .
We find that only 3 types of SED templates can produce such a red H - [ 3.6 ] color : a very dusty SED with the Calzetti extinction of A _ { V } =16 mag at z=0.8 ; a very dusty SED with the SMC extinction of A _ { V } =8 mag at z=2.0 \sim 2.2 ; and an 1Gyr SSP with A _ { V } \sim 0.8 at z=5.7 .
We argue that these sources are unlikely dusty galaxies at z \leq 2.2 based on absent strong MIPS 24 \mu m emission .
The old stellar population model at z > 4.5 remains a possible solution for the 4 sources .
At z > 4.5 , these sources have stellar masses of Log ( M _ { * } /M _ { \odot } ) =10.6 \sim 11.2 .
One source , ERS-1 , is also a type-II X-ray QSO with L _ { 2 - 8 keV } =1.6 \times 10 ^ { 44 } erg s ^ { -1 } .
One of the four sources is an X-ray QSO and another one is a HyperLIRG , suggesting a galaxy-merging scenario for the formation of these massive galaxies at high redshifts .