<p dir="ltr">This dissertation presents a analysis of negation in a spoken language, i.e., Khuzestani Arabic (KhA), and a sign language, i.e., Sadat Tawaher Sign Language (STSL). STSL emerged naturally without any intervention such as deaf education after a man lost his hearing around sixty years ago in a small village named Sadat Tawaher located in southwestern Iran. After this incident, the deaf person's family came up with a gestural system to communicate with him. Despite the fact that everyone in Sadat Tawaher, including the deaf person's family, speaks KhA, I hypothesized that KhA and STSL possess different grammatical ways to express negation. Data gathered using signed productions, story-telling, and grammaticality judgments clearly showed that negation is preverbal in KhA but sentence-final in STSL. </p>