PURPOSE: To improve the lipid constitution of egg yolk at a low cost in a short time and further nutritive value, by injecting an oil-soluble physiologically active substance or a fat or oil containing the same through eggshell into the egg yolk by a mechanical means.

CONSTITUTION: An oil-soluble physiologically active substance selected from linoleic acid, linolenic acid, arachidonic acid, vitamin A, D, E, or K, lecithin or β-carotene, or a fat or oil containing the same, e.g. purified sardine oil, is injected through eggshell into the egg yolk to give the aimed injected egg. As a specific method for injection, the following method may be cited: the eggshell is perforated with an electric drill for machining having a minute drill, and the substance is injected through the resultant hole using a syringe having such a length as to reach the tip thereof at the central part of the egg yolk, etc. Thus, the lipid constitution of the egg yolk is improved, and the content of the oil-soluble physiologically active substance can be increased in a short time.