Chemical compositions of four barium stars are studied. We obtain their {alpha}, iron peak and neutron-capture (n-capture) process element abundances. The atomic data and measured equivalent widths (EWs) of the related spectral lines are given. The abundance errors caused by the combined effects of the uncertainties in oscillator strengths loggf-values, equivalent widths (EWs) and stellar atmospheric parameters (e.g. effective temperature Teff, surface gravity logg, and microturbulent velocity {xi_t_}) are the total abundance uncertainties. The individual and total abundance uncertainties caused by these factors are given.