  All finite dimensional Nichols algebras with diagonal type of connected
finite dimensional Yetter-Drinfeld modules over finite cyclic group $\mathbb
Z_n$ are found. It is proved that finite dimensional Nichols algebra over
$\mathbb Z_2$ is a quantum linear space and Nichols algebra of connected
Yetter-Drinfeld module $V$ over $\mathbb Z_n$ with $\dim V >3$ is infinite
dimensional.
