Abstract: In this work mixed type power series spaces are introduced and some of  their properties are 

proved. The main result gives us some relations between a,b and  a,g if we have the condition 

.Also we have proved that there exists a Köthe space K(a) 

which is a subspace of (nuclear) and K(a) is not a quotient of (s), but the step-spaces of 

K(a) on the sets , subsets of N, are isomorphic to some finite type power series space. Some 

applications of this result on mixed type power series spaces and some corollaries are also contained.