In this paper，we examined the decision problems in a linear languages (for short LL) and Sequential languages (for short SL) for a Substitution. Following results are proved： Theorem 3 The problems of determining of given LL's (or SL's) L₁ and L₂ whefher or not there exists a substitution f mapping regular sets into regular sets is undecidable. Corollary 4 They are all undecidable to determine of arbitrary LL's (or SL's) L₁ and L₂ whether or not a f so that f(L₁)=L₂，where i) f is a homomorphism，or ii) f is a substitution，or iii)f is a ε-free substitution，or iv) f is a k-limited erasing substitution，or v) f is a generalized sequential machine，or vi) f is a complete sequential machine.