A1 B1
A2 B2
three one
two three

in A1 cell i need a formula


compare B1,A2,B2 in this 3 cell length of which cell is larger come string in A1

That is pretty basic:
=MAX(LEN(B1),LEN(B2),LEN(A2))
returns the greatest string length and:
=IF(LEN(B1)=MAX(LEN(B1),LEN(B2),LEN(A2)),B1,"")&IF (LEN(B2)=MAX(LEN(B1),LEN(B2),LEN(A2)),B2,"")&IF(LE N(A2)=MAX(LEN(B1),LEN(B2),LEN(A2)),A2,"")
returns the longest string(s).

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]