The purpose of this study is to model how to decide a quality of kelp product. The quality of kelp product is decided by numerical standard （length, weight and breath）and non-numerical standard （color and bentness）. It is difficult to estimate quality of kelp product, because non-numerical standard cannot be evaluated before drying. The quality classification in this study was carried out with 276 pieces of kelp from Fukushima area in Hokkaido which were graded by inspection institute. The authors assumed that the quality of kelp product is determined in two steps: numerical judgment and non-numerical judgment. The transition ratio between two steps was estimated. In this case, the grade of many kelp products went down in the second step. This transition suggests the necessity of reconsidering the management strategy.
