In this work, we study the effect of in-phase soliton interaction with and without the effect of third order dispersion (TOD) in 100Gbps telecommunication system. The relative spacing of soliton is chosen as 5.28 (qo) and their interaction is noted in one collision period or length (Lcoll). The soliton interaction without TOD is noted with β2=-2.55ps2/Km and with TOD near Zero Dispersion (ZD) point of -0.22ps2/Km. The effect of TOD decreases the interaction effect when noted with TOD value of β3=0.01 ps3/Km and further there was no interaction with high value of β3=0.1 ps3/Km. The main characteristic of TOD causing temporal shifts is noted in in-phase solitons where the higher deviation is noted with β3=0.1 ps3/Km than β3=0.01 ps3/Km. Further, we have also examined the effect of TOD with 3 and 6 solitons pulses to note the interaction effect. Finally it could be seen that when more than 2 soliton pulses are launched, TOD would degrade the system performance, where these adjacent pulses cross each other due to temporal shifts. © 2014 IEEE.