Marine insurance contracts, which intended to provide indemnity against marine risks upon the payment of price, known as a premium, originated in Northern Italy in the late 12th and early 13th centuries. The law and practice were later introduced into England through the Continent. It is, therefore, quite exact that English and European marine insurance law have common roots. Nevertheless, significant divergences between English and European insurance systems occurred since the late 17th century, mainly due to different approaches adopted by English courts. The rule of warranty in English marine insurance was developed and clarified in the second part of the 18th century by Lord Mansfield, who laid the foundations of the modern English law of marine insurance, and developed different approaches, especially in the field of warranty in marine insurance law. Since the age of Lord Mansfield, English marine insurance law has a unique rule on warranty. This article is, therefore, designed to analyse the overall rule of the rule of warranty in English marine insurance law. The result of analysis are as following. First, warranties are incorporated to serve a very significant function in the law of insurance, that is, confining or determining the scope of the cover agreed by the insurer. From the insurer's point of view, such the function of warranties is crucial, because his liability, agreed on the contract of insurance, largely depend on in, and the warranties, incorporated in the contract play an essential role in assessing the risk. If the warranty is breached, the risk initially agreed is altered and that serves the reason why the insurer is allowed to discharge automatically further liability from the date of breach. Secondly, the term 'warranty' is used to describe a term of the contract in general and insurance contract law, but the breach of which affords different remedies between general contract law and insurance contract law. Thirdly, a express warranty may be in any form of words from which the intention to warrant is to be inferred. An express warranty must be included in, or written upon, the policy, or must be contained in some document incorporated by reference into the policy. It does not matter how this is done. Fourthly, a warranty is a condition precedent to the insurer's liability on the contract, and, therefore, once broken, the insurer automatically ceases to be liable. If the breach pre-dates the attachment of risk, the insurer will never put on risk, whereas if the breach occurs after inception of risk, the insurer remains liable for any losses within the scope of the policy, but has no liability for any subsequent losses. Finally, the requirements on the warranty must be determined in according to the rule of strict construction. As results, it is irrelevant: the reason that a certain warranty is introduced into the contract, whether the warranty is material to the insurer's decision to accept the contract, whether or not the warranty is irrelevant to the risk or a loss, the extent of compliance, that is, whether the requirements on the warranty is complied exactly or substantially, the unreasonableness or hardship of the rule of strict construction, and whether a breach of warranty has been remedied, and the warranty complied with, before loss.