Mn doped ZnS nanocrystals have been successfully synthesized by mechanical alloying the stoichiometric mixture of elemental Zn, S and Mn powders at room temperature under inert atmosphere. Rietveld analysis of x-ray diffraction patterns of the samples confirms simultaneous presence of major zinc blende and minor wurtzite phases in milled samples. Phase transformation kinetics between these phases is established with milling time. Different microstructure parameters like lattice parameters, coherently diffracting domain (particle) size and r.m.s. lattice strain have been ascertained from the analysis. Distributions of crystallite size and r.m.s. lattice strain with milling time for both the phases have been revealed from Rietveld refinement. Band gap energy of milled samples with different milling time has been measured by UV-vis absorption spectra and photoluminescence emission spectra have also been analyzed. DC electrical conductivity of the semiconducting samples is measured and the conduction mechanism is explained by adiabatic polaronic hopping model.