We have examined solid solubility extension for melt-spun Cu-Ti alloys (4, 6, 7, and 8 mass% Ti) in comparison with that for conventional quenched alloys. X-ray diffraction (XRD) measurements revealed that the solid solubility extension for the melt-spun alloys was in the range of 7-8 mass% Ti, whereas that for quenched alloys was less than 6 mass% Ti. After annealing the melt-spun alloys at 673 K, the XRD measurements revealed sidebands with no intermetallic compound peaks, bright-field transmission electron microscopy images showed modulated structures, and selected-area diffraction patterns exhibited satellite structures; taken together, these experimental results confirm the occurrence of spinodal decomposition. In this study, however, distinct superlattice reflections were not observed.