In this paper, a solution is given to the problem proposed by Järvinen in [8]. A smallest completion of the rough sets system determined by an arbitrary binary relation is given. This completion, in the case of a quasi order, coincides with the rough sets system which is a Nelson algebra. Further, the algebraic properties of this completion has been studied.is a completion of (R * , ≤).In 1987, Gehrke and Walker [6] showed that the structure of the rough sets system determined by an equivalence relation R on U is isomorphic to 2 I × 3 J , where I = {R(x) | |R(x)| = 1} and J = {R(x) | |R(x)| > 1}. 2 I is the set of maps from I to a two element chain and 3 J is the set of maps from J to a three element chain. For reflexive relations R on U , the rough sets system determined by R can be order embed in (2 I × 3 J , ≤). Proposition 3.2. [8] If R is a reflexive relation on a set U , then (2 I ×3 J , ≤) is a completion of (R * , ≤), where I = {R(x) | |R(x)| = 1} and J = {R(x) | |R(x)| > 1}.