It is highly desirable to have a reliable modal parameter estimation technique with output-only measurements, especially for tall structures subjected to ambient wind loads. A modal identification technique called second-order blind identification (SOBI) is discussed in this paper to estimate the modal parameters of tall structures subjected to ambient loading. This method requires only acceleration time history data. The data are first preprocessed through cross-correlations to obtain the free response. SOBI uses these free responses to generate the mixing matrix (i.e., modal matrix) and sources, which are the modal responses of the structure. Even though SOBI has earlier been employed for modal parameter estimation, the majority of works attempt to solve small academic problems. Keeping this in view, we attempt to solve some practical engineering problems associated with tall structures. The proposed modal estimation technique is first evaluated using synthetic data of a 76-story tall benchmark building with varying levels of noise and later validated with the experimental data of the 610 m tall Guangzhou New TV Tower (GNTVT). Investigations carried out in this paper, using numerical and experimental ambient responses of tall structures, clearly indicate that the modal parameters estimated using SOBI are comparing very well with theoretical values.