Purpose : To determine the perturbation effect in the tissue downstream from surface layers of lesions located in the air/tumor-tissue interface of larynx using 6MV photon beam. Materials and Methods : Thermoluminescent dosimeters(TLDs), were embedded at 3 measurement locations in slab no. 7 of a humanoid phantom and exposed to forward and backward direction using various field sizes($4{ imes}4cm^2;-;15{ imes}15cm^2$). Results : At the air/tissue interface, forward dose perturbation factor(FDPF) is about 1.085 with $4{ imes}4cm^2,;1.05;with;7{ imes}7cm^2,;1.048;with;10{ imes}10cm^2$ and $1.041;with;15{ imes}15cm^2$. Backscatter dose perturbation factor(BDPF) is about 0.99 with $4{ imes}4cm^2$, 0.981 with $7{ imes}7cm^2$, 0.956 with $10{ imes}10cm^2$ and 0.97 with $15{ imes}15cm^2$. Conclusion : FDPF is greater as field size is smaller. And FDPF is smaller as the distance is further from the air/tissue interface.