Experimental investigations are conducted to study the effectiveness of protective coating with cashew nut shell liquid (CNSL) on coir. CNSL solution has been applied on suitably pretreated coir yarns and coating concentrations are optimized to reduce moisture absorption and microbial growth. Two common cellulose and lignin degrading fungi (Aspergillus niger and Rhizopus stolonifer) have been taken as test organisms. Qualitative and quantitative analyses are carried out tomeasure fungal growth on untreated and treated fibers. The study shows that treated fibers inhibit the development of fugal growth on fiber surface by 95%. The reducedmoisture absorption and improved hydrophobicity of the treated yarns are also reported. Increase in tensile strength up to 17% is noticed. The better properties achieved are explained on the basis of selection of the coating methodology and also the interfacial features of the coatings with the coir fiber. The results indicate the possibility of future application of such treated fibers in geotextiles having better performance compared to the untreated counterparts.