N-pentyl chitosan was prepared by the reaction with n-butyl aldehyde using different n-butyl aldehyde/chitosan ratio. Degree of substitution ($\%$) to amino group in chitosan gradually increased from 45.2 to 99.5 mol$\%$ for the n-butyl aldehyde/chitosan ratio from 1 to 5. The N-pentyl chitosan showed lower water contact angle and water retention value than original chitosan, indicating its higher hydrophobicity. From the evaluation of bonding strength with porcine skin, the N-pentyl chitosan showed higher bonding strength. This suggests that the hydrophobic interaction as well as the hydrophilic interaction plays an important role in bioadhesion.