A light guiding structure includes a light transmissive body and microstructures; the light transmissive body includes an upper conical groove and a lower accommodating groove, and the upper conical groove has a curved surface with a continually varied slope; the microstructures are disposed on the light transmissive body. A lighting device includes a circuit board, a light source and the aforesaid light guiding structure; the light source and the light guiding structure are disposed on the circuit board, and the light source is accommodated within the lower accommodating groove.