This question is basically just typos and confusion of variables:
allFiles = dir('*.xls'); % correct file extension
for ii = 1:size(allFiles, 1) % allFiles has one row per file, so loop over those
M{ii} = xlsread(allFiles(ii).name); % store matrix in cell array
end
Note that M
is now a cell array, because you can't store multiple matrices in a matrix or vector.