This study evaluated the depth of cure (DOC) of recently introduced resin composites for posterior use, bulk filled flowable composite (SureFil® SDR® flow DENTSPLY Caulk) at different depth. 30 specimens were prepared and divided into two Groups,Group 1: specimens with 2 mm depth, Group 2: specimens with 4mm depth. The composite specimens were prepared by using molds of different depth, one of them with was a hole of 4 mm depth and 4 mm internal diameter and the other was with a depth of 2 mm at the same diameter. The hole was bulk filled with SDR flowable composite resin and light cured for 20 seconds with a modern high-intensity LED curing unit (Elipar™ S10, 3M.US.), followed by 24 hours storage in complete darkness incubator at 37 C?. The degree of conversion was measured on the top and the bottom for both depths using Fourier transform infrared (FTIR) spectroscopy. A bulk filled flowable (SDR)revealed a significant difference in degree of conversion (DOC) when the bottom surface of the specimen witha 2mm depth (DOC=76.27112163) wascompared with the bottom surface of the 4mm depth specimen (DOC=73.92160935). The 2mm depth wasshown statistically significantly higher mean values degree of conversion than 4 mm depth (P-value = 0.032). There was no statistically significant difference in the degree of conversion mean values between the top and the bottom surfaces of the specimen of the same group (P >0.05). Upon the result of thisin vitro study, it was found that the degree of conversion of the SDR bulk-fill flowable resin compositewasaffected by depths. As the depth of the resin compositewas increased the degree of conversion was decreased.