Janusz Jan Sidło (19 June 1933 – 2 August 1993) was a Polish javelin thrower.

During his long career Sidło won 14 national titles and competed in five European Championships (1954, 1958, 1962, 1966, and 1969), winning them in 1954 and 1958 and medalling in 1969.

In October 1953, Sidło set a new European javelin record at 80.15 m in Jena.

He went to the 1956 Summer Olympics as a favourite, and was equipped with a modern javelin made of steel, while most of his competitors still used wooden ones.

Sidło led the competition with a throw of 79.98 m, but then lent his javelin to his poorly performing friend, Egil Danielsen from Norway.