Under the rapid economic development in which class stratification is being taken place among Japanese farmers, the viable farmers are enlarging their farm size and specializing their products. In other words, areal scale of production is widening and specialization in product is extending. This paper is a consideration on areal specialization of greenhouse horticulture with the following results. 1. Considering the national acreage of greenhouses by Prefecture, three Prefectures of Aichi, Shizuoka and Okayama occupy 61.7% of the total, showing a remarkable concentration and the distribution of greenhouse horticulture is also concentrated in those regions with a high population density along the Tokaido and San'yo railways, In greenhouse horticulture, melons grapes, chrysanthemums by electric lighting and carnations are the main products, each of which is remarkably specialized areally. In addition to this, the degree of regional accumula-tion and specialization in product is being intensified, and the large scale growing in the exist-ing greenhouse horticulture areas is contributing greatly to the increased products by green-house horticulture. 2. Taking examples of flower greenhouse growing areas in Aichi Prefecture, the Atsumi area in which chrysanthemums are grown in a large scale by electric lighting, is being pushed f oreward to organize the area, as a whole, for its production through co-operative marketing and consolidation of greenhouse sites. The Yokosuka area, Tokai-shi in which decorative plants are grown, is now being enforced to change the production method from the small-scale pro-duction of the variores species to be sold at higher prices for their scarcity to the mass produc-tion of a few species which have a greater popularity. But organizing the area in a large scale production method has been retarded in the Atsumi area owing to the scattered location of individual growing farmers. 3. Recent areal specialization in greenhouse horticulture has advanced by enlarging the size of existing horticultural farms but not by increasing the number of farms. The farmers are adapting the mass production method of specialized crops as farm size becomes larger. In the background, it can be noticed that the prices of flowers have been going upward accord-ing to the increased demand through both the popularization of flower consumption and the enlargement of marketing organization on one side, and the realization of mass production is largely due to the standardization of growing techniques and saving labour as well as sufficient labour equipped with a high still on the other. It is emphasized to say that the adaptation of the farmers to the national policies is the most important in establishing a highly specialized area in greenhouse horticulture.