With leading technology, then the sale can be done without meeting the seller to the buyer. Sales and purchases can be made through communications media such as telephone. As soon as buyers look at examples of things he wants, either via the internet, newspapers, brochures, then he can call the seller to order goods. Sellers noted that ordering and mail order form the basis of the transactions, so that the next item will be sent to the buyer where the buyer may have made the payment in advance as if we are ordering items advertised on TV, through DRTV, TVMedia or it could be the buyer pays to the seller when goods arrive at the buyer, as well as when we ordered fast food like Pizza HUT, Mc Donald, Hoka Hoka Bento and so forth. In that context, in practice, we often hear the term purchasing order. So the authors are interested in studying the purchasing order for the agreement in a transaction. The purpose of this study was to determine the characteristics of the PO (Purchase Order) / mail order as a purchase agreement and also to determine the payment obligations of the buyer to the seller if it refers only to mail order (PO). In this study, the authors conducted a study of normative law, which is a scientific activity, which is based on the methods, systematics, and certain thoughts, which aims to study one or more symptoms of a particular law, by way of analyzing it. The conclusion that the authors get is the first that the Purchase orders have the same elements with the purchase agreement. Second, since an agreement was reached that the basis of payment to be made the buyer to the seller