To obtain the subject ether, selected from specific hydroxylalkyl cellulosic compounds, thickening the coating material for which it is used to a minimum extent, improved in characteristics for preventing dripping, and useful as an emulsified coating material or the like.

This ether is selected from the group consisting of hydroxylalkyl cellulosic compounds substituted by 0.001 to 1.0, preferably 0.001 to 0.2, alkyl groups on the average per anhydrous glucose unit, and having 0.01 to 0.1 sulfoalkyl groups per anhydrous glucose unit, and preferably shown by formula l [(m) is 50 to 3,000; R1 to R3 are each a polyalkylene oxide chain shown by formula II (X is H or the like; and (p+q+r) is 1.3 to 4.5 on the average]. It is obtained by etherifying a celluiosic compound in the presence of a basic catalyst and etherification agent selected from the group consisting of alkylene oxides, and further etherifying it in the presence of an alkyl halide or alkyl glycidyl ether and sulfonate.