Ethylcellulose (EC) polymers with different hydroxyl content and molecular weight were synthesized in tetrabutyl ammonium fluoride/dimethyl sulfoxide medium. Their performance for demulsification of water-in-naphtha diluted bitumen emulsions was evaluated. It was found that EC with 4.5 wt % hydroxyl (degree of hydroxyl substitution, 2.4) is the most effective in demulsification. The demulsification efficiency of EC could be linked to its interfacial activity and potency of flocculation. The potency of flocculation by EC depends on its molecular weight and hydroxyl content, which affect molecular interactions. EC with higher molecular weight was found to be more effective in the demulsification of water-in-naphtha diluted bitumen emulsions.