A 2D liquid crystal system composed of hard particles shows phase transitions as thernpressure of the system varies. This fact was con_rmed by di_erent works done on 2Drnliquid crystal system di_erent shapes. These works done on hard particles of di_erentrnshapes con_rmed that particles of di_erent shapes show phase transition at di_erentrnpacking fractions. By understanding this idea, we are interested to study the phaserntransition of a system composed of hard triangles. We have considered NPT system withrndi_erent number of particles and used Monte Carlo method to study the phase transitionrnof the system. To study the phase transitions, we have considered the pressure, thernradial distribution function and the mean square displacement of the particles at di_erentrnpacking fractions. All of these results have shown as there is phase transition at _ _ 0:6rnand _ _ 0:9. The packing fraction at which the phase transition occurred didn't varyrnwith size of the system which shown the phases are stable at the thermodynamic limit. Asrnshown by previous work, if there is complete isotropic phase, the tetratic order parameterrns4 = 0 [20] but in our case the minimum value of tetratic order parameter was s4 _ 0:41rnwhich shows the non-existence of complete isotropic phase for hard triangles. For arnsystem of hard triangles, the phases observed during the phase transitions are: isotropicrnphase(when _ < 0:6), tetratic phase (when 0:6 < _ < 0:9) and solid phase (when _ > 0:9),rnand the plastic crystal wasn't observed.