It was the aim of the present study to investigate the potential of chitosan of different molecular weight in solution and as particles to enhance the transport into the brain. FITC-dextran 4 (FD4) transport with and without chitosans of different molecular weight across MDCK cell monolayers, a model for the blood brain barrier, was compared. In the following particles of chitosan exhibiting the most appropriate molecular weight were prepared and their particle size and stability were evaluated. Furthermore permeation studies, MDCK cell toxicity test and red blood cell lysis test were performed. The rank order for chitosan for permeation enhancement across MDCK cells was determined to be 20 kDa~150 kDa > 400 kDa~600 kDa. Moreover particles showed a higher permeation enhancement than the corresponding solution and the smaller the particles were the higher the permeation of FD4 was. All particles were stable for 72 h. Particles displayed increased MDCK cell toxicity and red blood cell lysis compared to chitosan in solution. The smaller the particles were, the higher their toxicity was. According to these results chitosan particles are more potent in absorption enhancement than chitosan solutions.