  We study the relaxation dynamics of electron distribution function on the
island of a single electron transistor. We focus on the 'interaction without
coherence regime in which an electron coherence can be neglected but quantum
fluctuations of charge are strong due to Coulomb interaction. The quantum
kinetic equation governing the evolution of the electron distribution function
due to escape of electrons to the reservoirs is derived. Analytical solutions
for time-dependence of the electron distribution are obtained in the regimes of
weak and strong Coulomb blockade. We find that usual exponential in time
relaxation is strongly modified due to the presence of Coulomb interaction.
