In this paper, we prove a conditional principle of Gibbs type forrandom weighted measures of the form ${L_n=\frac{1}{n}\sum_{i=1}^nZ_i\delta_{x_i^n}}$
, ((Zi)i being asequence of i.i.d. real random variables. Our work extends thepreceding results of Gamboa and Gassiat (1997), in allowing to consider thinconstraints. Transportation-like ideas are used in the proof.