A halo surrounding the edge-on Sb giant spiral galaxy NGC 4565 has been detected in the spectral band 3800–8600 A using a new photometric instrument, an annular scanning photometer. the halo is brightest close to the galactic nucleus and decreases in brightness until it reaches a level of 1 part in 1000 of the sky at a galactic radius of 6.1 arc minutes or 43 kpc from the galactic center. Because the scan path of the ASP is circular, this point corresponds to a distance of 34 kpc from the galactic plane. For comparison, the Holmberg radius of NGC 4565 is equal to 7 arc minutes or 50 kpc. Preliminary V-I photometric data indicate that the halo becomes redder with increasing galactic radius, exceeding V-I = 1.9. Based on a variety of possible origins for the light, it is concluded that the light is due to stars.