Single-molecule spectroscopy, combined with fluorescence resonance energy transfer, is utilized to study the conformational heterogeneity and the state-to-state transition dynamics of protein, DNA and RNA on the submillisecond to second timescales. However, observation of the dynamics on the microsecond timescale is still very challenging. This timescale is important because the elementary processes of structural dynamics of such biopolymer take place and direct comparison between experiment and simulation is possible. In this lecture, I talk about a new single-molecule technique which enables observation of the microsecond structural dynamics of bio-macromolecules through correlation of the fluorescence lifetime. This method, which we named two-dimensional fluorescence lifetime correlation spectroscopy (2D-FLCS), has been applied particularly to clarify the conformational dynamics of proteins, and conformational ensembles and the microsecond transitions in each ensemble are indicated, demonstrating the importance of quantifying microsecond dynamics of proteins on the folding free energy landscape.