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Let (Zn) be a critical branching process in an independent and identically distributed (i.i.d.) random environment. For each fixed environment ω, let Cn=Eω[Zn∣Zn>0] be the conditional expectation of Zn given Zn>0. We prove an analogue of Yaglom''s law: as n→∞, the conditional law of Zn/Cn, conditional on Zn>0, converges to a non-degenerate law on [0,∞). We give also an analogue of Kolmogorov''s law, as well as a local limit theorem for the semi-group of probability generating functions. To cite this article: Y. Guivarc''h et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003). [Copyright &y& Elsevier]