| C/1911 S3 (Beljawsky) | |
| Discoverer: | Sergei I. Beljawsky |
| Discovery Date: | 29 September 1911 |
| Designations: | 1911g 1911 IV |
| Epoch: | 11 October 1911 (JD 2419320.5) |
| Observation Arc: | 140 days |
| Obs: | 66 |
| Perihelion: | 0.3034 AU |
| Semimajor: | –2064.109 AU |
| Eccentricity: | 1.000147 |
| Inclination: | 96.466° |
| Asc Node: | 89.897° |
| Arg Peri: | 71.711° |
| Magnitude: | 1.0 (1911 apparition) |
| Last P: | 10 October 1911 |
Comet Beljawsky, formally designated as C/1911 S3, is a comet discovered by the Russian astronomer Sergei Ivanovich Beljawsky on September 29, 1911 and shortly thereafter, it was seen independently by four or five other observers in the United States and probably by others throughout the world. At the time it was discovered, the comet was near to the Sun which made observations difficult. However, several days after discovery it was a naked-eye object for a few days in the morning sky and later, after perihelion, as an evening object. It faded rapidly, becoming visible only in telescopes and was last seen on February 17, 1912. The comet sported a tail 8 to 10 degrees in length. In mid-October, the comet was visible in the evening sky together with another bright comet, C/1911 O1 (Brooks).
Comet Beljawsky is a non-periodic comet noteworthy for having a hyperbolic trajectory and so it is not expected to return to the inner Solar System.