Jeannette Josephina Maria ("Netty") Witziers-Timmer (July 22, 1923 – January 25, 2005) was a former Dutch athlete.
Born Jeannette Josephina Maria Timmer in Amsterdam her greatest success was when she won the gold medal in the 4 x 100 m relay at the 1948 Summer Olympics, together with Xenia Stad-de Jong, Gerda van der Kade-Koudijs and Fanny Blankers-Koen. Two years earlier, she had already won the same event at the 1946 European Championships.