The response of a lateral-torsionally coupled structure subject to dynamic wind loads can include the response for the along wind direction as well as that of the across and torsional directions. This study aims to propose a procedure to separate the modal responses from the lateral-torsionally coupled structural responses by using the independent component analysis(ICA) method and to effectively estimate the dynamic properties from the separated modal responses. The wind loads for the dynamic analysis of structure are generated from Karman wind speed spectrum for the along wind direction and an empirical overturning moment spectrum for the across wind direction. The kurtosis is introduced as the performance index for the mode separation by ICA. For the verification of the proposed method, a numerical simulation is performed. In the simulation, it is found that the lateral-torsionally coupled modal response can be separated precisely by ICA technique and very closely located modes can be also separated. From the numerical results, it is also shown that the modal properties such as natural frequencies and damping ratios are estimated effectively using the Hilbert transform and curve fitting, respectively. The results in this study show that the proposed method can be very usefully applied to the output-only system identification.