| Wim Thomassen | |
| Office: | Mayor of Rotterdam |
| Term Start: | 16 April 1965 |
| Term End: | 1 November 1974 |
| Predecessor: | Gerard van Walsum |
| Successor: | André van der Louw (Minus Polak acting) |
| Office1: | Mayor of Enschede |
| Term Start1: | 1 May 1958 |
| Term End1: | 16 April 1965 |
| Predecessor1: | Meine van Veen |
| Successor1: | Auke Johannes Vleer |
| Office2: | Mayor of Zaandam |
| Term Start2: | 16 May 1948 |
| Term End2: | 1 May 1958 |
| Predecessor2: | Joris in 't Veld |
| Successor2: | Gerrit Franken |
| Office3: | Member of the Senate |
| Term Start3: | 7 November 1961 |
| Term End3: | 10 May 1971 |
| Office4: | Member of the Provincial Council of North Holland |
| Term Start4: | 6 July 1954 |
| Term End4: | 1 May 1958 |
| Office5: | Member of the House of Representatives |
| Term Start5: | 31 July 1946 |
| Term End5: | 27 July 1948 |
| Birthname: | Willem Thomassen |
| Birth Date: | 1909 10, df=y |
| Birth Place: | Amsterdam, Netherlands |
| Death Place: | Bergen, Netherlands |
| Nationality: | Dutch |
| Party: | Labour Party (PvdA) (from 1946) |
| Otherparty: | Social Democratic Workers' Party (SDAP) (until 1946) |
| Spouse: | An Thomassen |
| Occupation: | Politician · Schoolteacher |
Willem "Wim" Thomassen [1] (3 October 1909 – 16 June 2001) was a Dutch politician of the Labour Party (PvdA).
Thomassen was born in Amsterdam. He was a schoolteacher and during World War II imprisoned by the Germans in Amsterdam from 1943 until January 1944.
After the war he was secretary of the Dutch People's Movement from August 1945 until July 1946.
On behalf of the Labour Party he was a member of the House of Representatives from July 1946 until July 1948.
Hereafter he was mayor of three municipalities: Zaandam (1948–1958), Enschede (1958–1965), and at last Rotterdam (1965–1974). In his last capacity he contributed significantly to the development of the Port of Rotterdam
Besides he was a member of the Provincial council of North Holland from July 1954 until May 1958, and a member of the Senate from November 1961 until May 1971.
His wife was also a schoolteacher. Wim Thomassen died at age 91 in Bergen (North Holland).