If gelatin is made from an unlawful substance, such as pig's meat, bones, skin, or the like, it is unlawful. Allah (Exalted be He) says:
Forbidden to you (for food) are: Al-Maitah (the dead animals - cattle - beast not slaughtered), blood, the flesh of swine
Religious scholars unanimously agreed that lard (pig's fat) falls under this prohibition. However, if the gelatin is free from any unlawful substance, there is no harm in using it. (Part No. 22; Page No. 261) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.