By diffusion we can say that matter is made up of very small sized particles and by Brownian motion, we can say that particles of matter are in constant motion.
During diffusion particles of matter possess kinetic energy whereas during Brownian motion the particles possess inter molecular space.
Particles of matter continuously moving around in a random manner is termed as Brownian motion. This movement helps the particles of two or more different types of substances to mix with each other and this process is termed diffusion.