Abstract: Disclosed in a straw-insertable lid for a paper cup which is placed on an upper end of a paper cup in which a beverage such as tea, coffe, a soft drink, fruit juice, or the like, a sherbert-like beverage of any of these beverages, or the like is accommodated singly or together with crushed ice so as to allow the beverage to be drunk by inserting a straw through the straw-inserting slit provided in the top plate portion. The upper lid is formed of natural rubber, and a protruding outer ring is provided on the top plate portion around the slit. As a result, when the lids are disposed of by being dumped as rubbish after use, the lids easily decompose, thereby preventing the dumped lids from constituting a source of environmental destruction. At the same time, when the straw is inserted through the slit, the protruding annuular ring prevents the slit from becoming easily being ripped large.