This paper scrutinizes the impacts of demand-side resources (DSRs) on the power system reliability via a novel multi-target generation maintenance (GM) model. The nominated model uses the Lexicographic preferences to hierarchically consider the environmental issues, economics, and reliability of power systems. In this regard, the produced emission, which reflects the per unit produced pollutant values in different locations, is minimized. Taking into account the environmental constraints, the total incurred expenditures, including operating and maintenance costs, reserves costs, and total incentives are also minimized. Subsequently, the GM problem considering the correlation constraints is handled while the reliability index, the average net reserve value (ANRV), is maximized over the scheduling horizon. The DSRs improve the system reliability such that the total costs, and emission level, do not exceed the situation in which DSRs are not available. The GM scheduling is a highly complicated problem and considering DSRs makes it even more complicated. To handle this problem more efficiently, appropriate linearization technique is used, while the proposed model is formulated in GAMS modeling language. To evaluate the capability of DSRs in system reliability improvement, the modified 24-bus IEEE-RTS is conducted. Results indicate that by selecting proper location and incentives, significant improvement is obtained. Nomenclature Indexes and Sets b Bus index. i Unit index. l Transmission line index. N , N , N , N Number of units, units in region R, buses, and lines, respectively. N , N , N Number of segments to linearize emission, cost, and incentive curves, respectively. t Time index.