Uninorms were introduced by Yager and Rybalov [13] as a generalization of triangular norms and conorms. We ask about properties of increasing, associative, continuous binary operation U in the unit interval with the neutral element e∈[0,1]. If operation U is continuous, then e=0 or e=1. So, we consider operations which are continuous in the open unit square. As a result every associative, increasing binary operation with the neutral element e∈(0,1), which is continuous in the open unit square may be given in [0,1)2 or (0,1]2 as an ordinal sum of a semigroup and a group. This group is isomorphic to the positive real numbers with multiplication. As a corollary we obtain the results of Hu, Li [7].