Let X 1 , ..., X n be a random sample from an absolutely continuous (with respect to Lebesgue measure) distribution with the corresponding generalized order statistics X(1, n,m, k), ..., X(n, n,m, k). In this paper, we present some characterization of distributions when linearity of regression E [X(s, n,m, k)|X(r, n,m, k) = x] = ax + b is identified.