Mussel adhesive protein (MAP) is expected to be used as a new artificial adhesive material for bonding under wet conditions such as surgical incisions. The adhesive strength of MAP, however, has not been accurately measured until now for practical use. The study aims to clarify the time variation of adhesive strength from an engineering perspective. Adhesive strengths have been measured during the range from ready to one month after adhesion setup, using prototype peel test procedure. The results show that the adhesive strength depends on time and repeated seesawing strength with the elapse of days.