The object of this article is to point out, analyzing chiefly the administrative tablets from Lagash, some characteristics of agricultural production in ancient Sumer and to explain how closely these characteristics were related to the collective labor-system.This paper consists of three parts. In the first chapter, I illustrated the productivity of the fields in Lagash. 6 gur-sag-gal 49 sila per bur (2179.1l per ha) and 76.1-fold of sowing amount, the figures which I gained from RTC71 and DP574 written in the same year, can be regarded as the average land and seed-productivity of barley in Lagash at the end of the Early Dynastic Period.But fertility declined greatly by the time of the Third Dynasty of Ur. My estimate of 30 gur-lugal per bur (1193.2l per ha) was obtained from RTC407 in which were written the total area of directly-controled fields of barley in Lagash at that time, the amount of barley expected to be yielded from this area and lastly the amount actually yielded. As 1.5 gur-lugal of barley was sowed per bur, seed-productivity was 20-fold. Th. Jacobsen and R. M. Adams think salinization of soil to be the cause of decline in fertility. But what brought about salinization still remains unsolved.At any rate, 20-fold at the period of the Third Dynasty of Ur is still higher than the figures reported about Italy in the Roman period. And 76.1-fold at the end of the Early Dynastic Period shows clearly the extraordinary fertility of Sumer. This was possible, of course, only by the elaborate irrigation-system.In the second and third chapter, I discussed the character of irrigating-works in Sumer. To begin with, I dealed with the so-called ‘Farmers' Almanac’ in which were described various advices for a good harvest given by a farmer to his son. The farmer gives his son many, sometimes too trifle, advices about the agricultural activities at the time of preparing land, sowing and harvesting. To irrigate three or four times according to the growth of barley is, however, the only one instruction by him about the period between sowing and harvesting. That is to say, a good harvest could be expected in ordinary years only by doing such works during the interval period. Naturally it was chiefly between sowing and harvesting that people were engaged in the collective irrigating-labor. In fact, we know from CT III 18343, a large Lagash-tablet of the Third Dynasty of Ur, that erin-people worked exclusively at the ditches of various fields and canals from the seventh month to the twelfth, roughly between sowing and harvesting.A further study must be made about the interrelations between agricultural production and collective labor-organization, because ‘the pattern of despotism in Sumer’ will be defined by these two fundamental factors of sumerian society.