In this paper, optimal P and PI controllers are proposed for level control of single tank system. The integral-square-error (ISE) of unit step response is considered as design criterion for obtaining optimal controller settings. This method of formulation of ISE requires only some alpha and beta parameters unlike integration with time. The teacher learner based optimization (TLBO) algorithm is employed for minimizing the performance index. It is found that the proposed TLBO based controllers provide excellent results in terms of time domain specifications.