This paper presents stability analysis of wind farms in frequency domain. The interaction between the wind turbine control system and the wind farm structure in wind farms is deeply investigated. Two wind farms (i.e. Horns Rev II and Karnice) are taken in to consideration in the study. It is shown that wind farm components such as long HVAC cables and park transformers can introduce significant low-frequency series resonances seen form the wind turbine terminals which can affect wind turbine control system operation and overall wind farm stability. The same wind turbine converter control strategy is evaluated in two different wind farms. It is emphasized that the grid-side converter controller should be characterized by sufficient harmonic/noise rejection and adjusted depending on wind farms to which it is connected. Various stability indices such as gain margin, vector gain margin, and phase margin are used in order to emphasize differences between the two wind farms.