I haven't found "the" definitive answer to your question, but we can infer an
answer based on other similar limitations in Excel.

Various formulas have limits to the number of parameters they can handle.
For example, the CONCATENATE() function has a limit of 32 parameters. There
is also a limit to other things such as the length of a formula and levels of
nesting.

I suspect you've found the undocumented(?) limit to the number of parameters
in LOOKUP() as you've tried to use it.

As smartin indicated, for large lists like that you're probably better off
setting up some columns as a table, either on the same sheet or another, and
using VLOOKUP() to get your results.

"Lookup formula limitation?" wrote:

I have 160 number in column A and 160 numbers in Column B.....

Lookup let me to compair only 80?
=lookpu(A1,{1,2,3,4,5.........160},{10,20,30,..... .......1600})

How come excel let me do up to 80, not 160?