To obtain the subject composition dispensing with specific adjustments of a specific gravity, weight and the like regarding additive pellets, having excellent peptidizing property and constant feeding property, capable of giving a master batch which can be diluted at a high dilution ratio and enabling the addition to a resin to be added by a base color method.

The subject composition comprises a thermoplastic resin composition containing an additive characterized in that, in a master batch to be used in a feeding method, when the shape of a pellet is measured in the longitudinal direction (y), the lateral direction (x) and the vertical direction (z), the total of their maximum values, that is, the value of (x)+(y)+(z) is 4.6 mm or less, and the total of their minimum values is 0.9 mm or more; each of (x), (y) and (z) is 20% or more of their total; the orthogonal projection of the pellet is quadrate or rectangular; when two or more different compositions are used in a mixture, the ratio of the lengths of the adjacent two sides of an orthogonal projection is from 1 to 1.4, and letting the average and the standard deviation of the totals (n=10) of the lengths of the two sides which are obtained by measuring at 10 different points be (a) and (b), respectively, the value, (b)/(a), does not exceed 0.1.