Nanoscale dual-wavelength lasers are attractive for their potential applications in highly integrated photonic devices. Here we report the growth of nanoribbon lateral heterostructures made of a CdSxSe1-x central region with epitaxial CdS lateral sides using a multistep thermal evaporation route with a moving source. Under laser excitation, the emission of these ribbons indicates sandwich-like structures along the width direction, with characteristic red emission in the center and green emission at both edges. More importantly, dual-wavelength lasing with tunable wavelengths is demonstrated at room temperature based on these single-nanoribbon heterostructures for the first time. These achievements represent a significant advance in designing nanoscale dual-wavelength lasers and have the potential to open up new and exciting opportunities for diverse applications in integrated photonics, optoelectronics, and sensing.