This thesis attempts to investigate the Meditation on the Foul based on the overview and the structure of overall meditation instructions. This starts with a discussion of the four foundations of mindfulness and their practices. Then it focuses on expounding the content and characteristics of mindfulness of the body. There are 6 practices included in the mindfulness of the body. In order to highlight the teaching points of the meditation on the foul in the Visuddhimagga, this thesis emphasizes A-śubhā-smrti and Navasivathika (visualization on 9 or in some texts, 10 stages of decaying corpses). The object of the two Meditations on the Foul is the form aggregate, one of the 5 aggregates. The aggregate of form belongs to the category of mindfulness of the body in the four foundations of mindfulness. There are clear purposes on the path for practicing these types of contemplations. These contemplations are considered conducive in overcoming desire and lust. As a result, one will gain meditative absorption, develop siddhis and eventually reach ultimate liberation. The point of practicing Meditation on the Foul is to develop steady recollection of aversion. The goal is for a practitioner to focus uninterruptedly on an object and in this case to make sure that Saṃvega (the aspiration to be liberated from samsara and escape the suffering of this world) keeps arising. The main purpose of practicing A-śubhā-smrti and Navasivathika is to let go of desire and lust. The teaching point of Navasivathika (the cemetery practice visualizing decaying corpses) is obvious. The procedure involves one leaving one's house and walking to a cemetery to view corpses. During the process of coming and going, one is required to pay attention and recollect everything that is noticed, including the decaying corpses. The cemetery and corpses are rather dreadful, the scope of examination and recollection is wide and complicated and the state of corpses changes rapidly. To properly practice this meditation and be able to recollect everything that happens during it, one must carefully prepare and make great effort to keep all the steps and details in mind. Should one fail to recall the details of what they have noticed, it would be a loss of a rare opportunity. The complexity of this meditative practice is precisely why it is thought to be more important than others.