Section 55 (1) of the Marine Insurance Act 1906 states that the insurer is liable for any loss proximately caused by a peril insured against but is not liable for any loss not proximately caused by a peril insured against. It is, therefore, essential to determine whether it is to be recoverable under the Marine Insurance Policy attaching the Institute Cargo or Hull Clauses. But a number of important losses are excluded from the policy by subsection 2 of the same section, unless the policy otherwise provides, although these losses are proximate causes of them. The purpose of this study is to investigate the meaning of proximate cause and excluded losses in the Act. The method of this study is a literature survey. In summary, (1) if the loss is considered to have been proximately caused by a certain peril, and the peril is insured against, the claim is recoverable, (2) if there are different causes resulting in separate losses, the claims recoverable will be those due to insured perils, (3) when the effective cause of the loss is established, remote causes can be ignored, (4) when causes of loss are combined, the claim is recovera-ble if the cause which is proximate in efficiency is an insured peril, (5) if there are two causes, equal in efficiency, the loss is recoverable if one of the causes is an insured peril, but always providing the other cause is merely an uninsured peril rather than a specific exclusion, (6) although certain losses are exclu-ded by section 55 (2) of the Act, with the exception of wilful misconduct of the insured, it is permitted for provision to be made in the policy to widen the terms to include such losses.