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The Cu-Ti-Si alloys containing in-situ formed Ti5Si3 are prepared. In order to clarify the Ti5Si3 formation processes and its microstructure characteristics, the as-cast and deeply etched Cu-Ti-Si alloys with different compositions and cooling rates were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is found that the eutectic Ti5Si3 phases in Cu-Ti-Si alloys are rod-like with hexagonal cross section which tend to intertwine with each other to form a firm skeleton like a bird nest structure which can make the alloys keep their original shape even after etching off the Cu matrix. In addition, there is Cu in the center of many Ti5Si3 rods, resulting in a core-shell structure. With the increase of the cooling rate, Ti5Si3 distributes more uniformly, and the diameter of Ti5Si3 significantly decreases, with a minimum size of less than 100 nm, while the aspect ratio of Ti5Si3 increases. [ABSTRACT FROM AUTHOR]