Jeannette Josephina Maria "Netty" Witziers-Timmer (July 22, 1923-January 25, 2005) was a former Dutch athlete.

Born Netty 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.