\documentclass{article}

 \usepackage{rotating}
\begin{document}
\begin{tabular}{|c|c|}
\hline
{\begin{sideways}aaaaa \end{sideways}}  &  {\begin{sideways}12345\end{sideways}}\\ 
\hline
{\begin{sideways}aaaaa \end{sideways}}  &  {\begin{sideways}12345 \end{sideways}}\\ 
\hline 
\end{tabular} 
\end{document}