Reliability index is a parameter that shows the level of service or level of reliability of electricity supply to consumers. The Gedong Kuning substation is a substation that supplies electrical energy to DIY and several regions in Central Java. Network distribution of the Gedong Kuning substation area was felt to be a problem. Therefore, further research is needed to find out the reliability of the Gedong Kuning substation. The method used in this study is the calculation of VOLL (Value Of Loss Load) and EENS (Expected Energy Not Supplied). The results of this study obtained VOLL values in 2014 of 33.57 Rp / Kwh and 2015 of 33.63 Rp / Kwh. The average value of EENS in 2014 was Rp. 56.153.170 And in 2015 it was Rp. 56.153.170 based on VOLL and EENS compared to SPLN in the Gedong Kuning substation categorized as still reliable.