Giant submandibular sialolithiasis is uncommon and sialoliths causing sialo-oral fistula are rare. We report a case of giant Wharton's duct sialolithiasis causing sialo-oral fistula in a 40 years male who presented with pain and swelling over right side of floor of mouth for more than two years and visualisation of yellow coloured stone like structure at floor of mouth in the last two days. With diagnosis of Submandibular gland sialolithiasis with sialo-oral fistula, sialolithotomy and marsupialization of Wharton's duct was done under local anaesthesia.