Roller compaction is a continuous dry granulation process, in which powder is compressed by two counter-rotating rollers. During this process, the powder feeding to the compaction zone has a significant effect on product quality. This work investigates the flow of powder from the feeding zone to the compaction zone using online infrared thermography as Process Analytical Technology (PAT) which is achieved via a specially built cheek plate (side-sealing). The powder undergoes increasing stress from the rollers when it is approaching the minimum gap of the compaction zone, which can be indirectly monitored by measuring the powder temperature. The online monitoring of the powder flow during the roller compaction helps locate the nip region and identify the effect of different roller forces on the temperature of the feeding powder. The results show that the nip region can be identified by analysing the temperature profiles from the feeding to the compaction zone. The increase of roller force results in an increasing slope of the powder temperature profile. In addition, offline X-ray CT measurement results show the increase of density along the feeding to the compaction direction, which is compared with Johanson theory under different roller forces in the roller compaction process.