Thunder of Gigantic Serpent(1988)

A secret formula that can cause plants and animals to expand a thousand-fold in size is stolen by a terrorist group. During a wild chase and shoot-out, the formula is lost. It's found by a little girl who accidently gives the formula to her pet snake. After the snake grows to an immense size, it follows and protects her. When the terrorists go after the girl, the snake begins destroying everything in its path.