Different aspects of agglomeration behavior of cohesive particles during fluidization have been studied in the present work. This work also helps in determining the agglomerate size during fluidization. Experiments were performed on both coarse particles and fine powders. The fluidization behaviors of these particles were thereby studied and effects of gas velocity on agglomerate size are also studied out by varying gas velocity, temperature and bed materials. Binding property of bed material plays a very important role in formation of agglomerates of cohesive particles in fluidized bed. Experimental and theoretical results indicate that agglomerate size tends to attain smaller size as the velocity of particle is increased.