PURPOSE: To prepare a soft capsule having a water-containing fluid material in it, and warm water solubility, by using a fluid material containing a mono- or bivalent metal ion as a capsule core substance, and carrageenan as a capsule covering substance.

CONSTITUTION: A fluid material containing ≥1mol mono- or bivalent metal ion (e.g., K ion, Na ion, or Ca ion) in an aqueous section is used as a capsule core substance, and K-carrageenan is used as the whole or part of a capsule covering substance. The concentration of K-carrangeenan is about 1W12wt%, and the fittest condition is varied with the thickness, strength, and hardness of a film. The soft capsule is formed by a conventional procedure by rotary method, dropping method. Consequently, the soft capsule having stably a water-containing fluid material, and warm water solubility is prepared.