The fuzzification of $a\&\mathcal I$-ideals 
in {\bf IS}-algebras is considered. Relations 
between fuzzy $p\&\mathcal I$-ideals and fuzzy
$a\&\mathcal I$-ideals are stated. 
Characterizations of fuzzy $a\&\mathcal I$-ideals 
are given. Extension property for fuzzy
$a\&\mathcal I$-ideal is established.