In this paper, 
we study the  weak  convergence of Mann's type  
iteration procedure and 
the existence of nonexpansive  retractions
for commutative  semigroups in Banach spaces which satisfy  Opial's
condition.
Further, we introduce 
an implicit iteration  procedure
for  nonexpansive semigroups and then
prove  a strong  convergence theorem
for the nonexpansive semigroups in general Banach spaces.