Janusz Sidło (June 19, 1933 in Katowice-Szopienice – August 2, 1993 in Warsaw) was a Polish athlete, who competed in the javelin throw. He was awarded the Officer's Cross of the Order of Polonia Restituta and later the Knight's Cross.

Sidło was multiple Polish champion (14 times) in javelin. He participated in five Olympic Games (1952, 1956, 1960, 1964, and 1968), and five European Championships in Athletics (1954, 1958, 1962, 1966, and 1969).

In October 1953, he broke the European record (80.15) in Jena. Sidło won two gold medals at the European Championships (Bern 1954 and Stockholm 1958). In June 1956, he set the world record (83.66) in Milan. Sidło went for the Olympic Games in Melbourne as a favourite. He had been leading the competition with the distance of 79.98 m and was close to the Olympic gold when he decided to lend his modern javelin to his friend, Egil Danielsen, who had been performing poorly. With the Pole's javelin Danielsen achieved the new world record of 85.71 m and won the gold medal, pushing Sidło down to the second place. Sidło's behaviour is considered one of the most beautiful fair play gestures in Olympic history.

In 1960, he took 8th place in the 17th Olympic Games at Rome. In 1962, he took 7th at Belgrade (7th EU-ch). In 1964, he took 4th at Tokyo (18th Ol). In 1966, he took 7th at Budapest (8th EU-ch). In 1968, he took 7th at Mexico City (19th Ol). In 1969, he won bronze medal at Athens (9th EU-ch).