Tannins are secondary plant compounds frequently encountered in tropical feeds. They are known to complex with proteins, thus reducing the availability of protein to ruminants. Tannin determination is thus a crucial factor when estimating the feed quality of tropical plants. Bovine serum albumin (BSA), which is commonly used in tannin binding assays has the drawbacks of being a non-plant protein and requires a rather low pH (4.9, iso-electric point of BSA) for complex formation with tannins. Papain is a commercially available pure protein from Carica papaya that may be a suitable alternative. This study evaluates papain as a test protein in a tannin binding assay in comparison to BSA by determining the specific protein precipitation capacity (sPPC) of the tannin rich plants, Salix alba (salix) and Rhus typhina (sumach). Salix and sumach leaves contain exclusively condensed tannins and hydrolysable tannins respectively.