This answer is assuming that the question refers to the wrinkle relaxing effect of Botox in facial treatment, such as frown lines.
The maximum effect is reached in about 2 weeks. Your facial expression will become more relaxed but by no means mask like. The overall effect is very natural if a well balanced treatment is done. The effect of treatment generally lasts for 3 months. You will notice a steady fading of its effects. Re-treatment is then required.