Single-frequency lasers in the blue-green (500 nm) visible spectrum are important for many applications including iodine precision spectroscopy, optical frequency standards or ionized argon lasers substitution. To the best of our knowledge, we report in this paper the first single-frequency diode-pumped Ytterbium-doped solid-state laser operating at 501.7 nm by intracavity second harmonic generation (SHG). The singlefrequency fundamental infrared laser light is generated by a diode-pumped Yb3+:Y2SiO5 crystal in a ring oscillator. Intracavity SHG with a KNbO3 nonlinear crystal produced more than 50 mW of single-frequency bluegreen radiation