Oral squamous cell carcinoma (OSCC) is the most frequent malignancy of the oral cavity. Squamous cell carcinoma of floor of the mouth during pregnancy is not reported in the literature. 26-year-old female patient admitted to our clinic with a lesion in the mouth for 2 weeks. The patient was 34 weeks pregnant and non-smoker. ENT examination revealed that the fragile, ulcerated, 2×1 cm width and 6-7 mm depth lesion was on the left side of the floor of mouth. In eight days, the tumour was almost double in size. Median mandibulotomy was applied to facilitate the resection of the tumor via transmandibular way and the tumour was removed en bloc together with the neck dissection specimen. The patients with oral squamous carcinomas during pregnancy should be treated more quickly, patients and families should be informed about the tumor progression.