The PL spectra for the 10, 4.5, 3.5, 3,1nm sized ZnS:Mn~2+ nanoparticles and corresponding bulk material under different pressures were investigated. The orange emission band originated from the 4T 1-6A 1 transition of Mn~2+ ions showed obvious red shift with the increasing of pressures. The pressure coefficients of Mn-related emissions measured from bulk, 10, 4.5, 3.5 and 3nm samples are -29.4±0.3, -30.1±0.3, -33.3±0.6, -34.6±0.8 and -39±1 meV/GPa, respectively. The absolute value of the pressure coefficient increases with the decrease of the size of particles. The size dependence of crystal field strength Dq and Racah parameter B accounts for the size behavior of the Mn-related emission in ZnS:Mn nanoparticles. The pressure behavior of Mn-related emission in the 1 nm sized sample is somewhat different from that of other nanoparticles. It may be due to smaller size of 1 nm sample and the special surface condition since ZnS nanoparticles are formed in the cavities of ziolite-Y for the 1 nm sample.