Context :

Aims : Superclusters are the largest relatively isolated systems in the cosmic web .
Using the SDSS BOSS survey we search for the largest superclusters in the redshift range 0.43 < z < 0.71 .

Methods : We generate a luminosity-density field smoothed over 8 ~ { } h ^ { -1 } \mathrm { Mpc } to detect the large-scale over-density regions .
Each individual over-density region is defined as single supercluster in the survey .
We define the superclusters in the way that they are comparable with the superclusters found in the SDSS main survey .

Results : We found a system we call the BOSS Great Wall ( BGW ) , which consists of two walls with diameters 186 and 173 h ^ { -1 } Mpc , and two other major superclusters with diameters of 64 and 91 h ^ { -1 } Mpc .
As a whole , this system consists of 830 galaxies with the mean redshift 0.47 .
We estimate the total mass to be approximately 2 \times 10 ^ { 17 } h ^ { -1 } M _ { \odot } .
The morphology of the superclusters in the BGW system is similar to the morphology of the superclusters in the Sloan Great Wall region .

Conclusions : The BGW is one of the most extended and massive system of superclusters yet found in the Universe .