Abstract: Using a TES-135A color meter, 160 samples of bedding material from the microbial fermentation beds in pig pans were measured. The chromaticity data were fed to the Hunter's color difference formula, △E=(△L)²+(△a)²+(△b)²1/2, to obtain the △E value. Based on the average value (μ) and dispersion degree (σ) of △E, the stages of fermentation of the bedding material were classified. The 1^st stage ranged from 0 to μ-2σ, the 2^nd stage from μ-2σ to μ, the 3^rd stage from μ to μ+2σ, and the 4^th stage beyond μ+2σ. Subsequently, the apparent color, humidity, odor, and degree of decomposition were determined for samples from each fermentation stage. A regression analysis showed a high correlation between the colorimetric measurements and the observations suggesting the color meter might be used as a means to rapidly determine the fermentation stages of a microbial fermentation bed in a pig pan.