The present invention relates to water-soluble natural film and its preparing method. More particularly, the present invention relates to water-soluble natural film manufactured by dissolving as an active ingredient a water-soluble chitosan prepared in such a manner that chitin/chitosan decomposed with lysozyme is rinsed with ethanol, subjected to electric adjustment and sonication in a saline solution and to ion-exchange to obtain water-soluble -glucosamine fibrin followed by nano-sized coating the -glucosamine fibrin with immunoglobulin (-globulin), and seaweeds and functional ingredients in distilled water and gelatinating. The water-soluble natural film according to the present invention, unlike the conventional film containing chitosan, comprises, at a predetermined content ratio, chitosan with improved water solubility and immunity, seaweeds and functional ingredients. Therefore, it imparts elasticity to matrix of a film to enable film molding with convenience and renders more compatibility to human body due to natural materials as its active ingredients, eliciting more favorable feeling when taken in. In particular, the film composition itself is processed to form a film with a desired thickness and size or is coated on a conventional biodegradable resin film, being applicable to a film in preparing an oral cleaning agent with immediate effect and a food packaging material.