In this study , we present long term photometric variations of the close binary system GO Cyg .
Modelling of the system shows that the primary is filling Roche lobe and the secondary of the system is almost filling its Roche lobe .
The physical parameters of the system are M _ { 1 } = 3.0 \pm 0.2 M _ { \odot } , M _ { 2 } = 1.3 \pm 0.1 M _ { \odot } , R _ { 1 } = 2.50 \pm 0.12 R _ { \odot } , R _ { 2 } = 1.75 \pm 0.09 R _ { \odot } , L _ { 1 } = 64 \pm 9 L _ { \odot } , L _ { 2 } = 4.9 \pm 0.7 L _ { \odot } , and a = 5.5 \pm 0.3 R _ { \odot } .
Our results show that GO Cyg is the most massive system near contact binary ( NCB ) .
Analysis of times of the minima shows a sinusoidal variation with a period of 92.3 \pm 0.5 years due to a third body whose mass is less than 2.3 M _ { \odot } .
Finally a period variation rate of -1.4 \times 10 ^ { -9 } d/yr has been determined using all available light curves .