In this paper, we introduce the quaternionic slice polyanalytic functions and we prove some of their properties. Then, we apply the obtained results to begin the study of the quaternionic Fock and Bergman spaces in this new setting. In particular, we give explicit expressions of their reproducing kernels.Proposition 3.18. Let Ω be an axially symmetric domain and let f : Ω −→ H be a slice polyanalytic function. Assume that there exist J, K ∈ S, with J = K and U J , U K two subdomains of Ω + J and Ω + K respectively where Ω + J := Ω ∩ C + J and Ω + K := Ω ∩ C + K . If f = 0 on U J and U K , then f = 0 everywhere in Ω. Proof. Let f be a slice polyanalytic function on Ω such that f = 0 on U J and U K . Thus, since U J and U K are respectively subdomains of Ω + J and Ω + K . It follows, from the Splitting Lemma for slice polyanalytic functions combined with the classical complex analysis that f = 0 everywhere on Ω + J and Ω + K . Then, we just need to use the Representation Formula which allows to recover a slice function by its values on two semi-slices to complete the proof.