The tribological performances of diisobutyl phthalate, dipentyl phthalate, dinoctyl phthalate, di(2ethylhexyl)phthalate, dinonyl phthalate, and diisodecyl phthalate were investigated under the loads form 5 N to 98 N. The results show that the friction coefficients of the six esters tend to decrease with the increasing of the time at the different loads. Among the six phthalate esters, diisodecyl phthalate shows the lowest friction coefficient under the all loads, however whose friction coefficient is changed greatly under the low loads(about 5 N). Under the same loads, the average friction coefficients of straight chain esters is decreased with the increasing of the carbon chain length, however the branched chain esters present different trend. The wear scar diameter of the esters is increased with the increasing of the loads. Under the same loads, the wear scar diameter of the different esters show no obvious change rule, indicating the extension of carbon chain length cannot contribute to reduce the wear scar diameter.