  Two-dimensional (2D) superconductors supply important platforms for exploring
new quantum physics and high-$T_c$ superconductivity. The intrinsic
superconducting properties in the 2D iron-arsenic superconductors are still
unknown owing to the difficulties in the preparation of ultrathin samples. Here
we report the fabrication and physical investigations of the high quality
single-crystalline ultrathin films of the iron-arsenic superconductor
KCa$_2$Fe$_4$As$_4$F$_2$. For the sample with the thickness of 2.6$\sim$5 nm
(1$\sim$2 unit cells), a sharp superconducting transition at around 30 K (onset
point) is observed. Compare with the bulk material, the ultrathin sample
reveals a relatively lower $T_c$, wider transition width, and broader flux
liquid region under the in-plane field. Moreover, the angle dependent upper
critical field follows the Tinkham model, demonstrating the two-dimensional
superconductivity in ultrathin KCa$_2$Fe$_4$As$_4$F$_2$.
