Samples of groundnut cake (GNC) were dry heated in a forced air oven at 115, 130 and 145 for 20, 40, or 60 minutes. Other samples were heated at 160 or 175oC for 20 and 40oC. Protein quality was evaluated by: in vitro ammonia production, in situ dry matter (DM) and nitrogen (N) disappearance, acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent fiber nitrogen (ADF-N) concentration. In vitro ammonia production was reduced by heat treatment. Mean in vitro ammonia concentration declined linearly as temperature increased from 145 to 175o and exposure time increased from 20 to 60 minutes. N and DM in situ disappearance decreased from 96 to 52% and from 74 to 48%, respectively, as heating of PNM increased from 115 to 175oC for 20 minutes. ADF increased from 9.8% to 11.8%, NDF increased from 18 to 31%, hemicellulose increased from 8.1 to 19.2% and ADF-N increased from 0.61 to 1.2% as temperature increased from 115 to 175oC for 40 minutes. The significant increase in ADF, NDF, ADF-N and hemicellulose observed in this study and the decreased solubility of DM at the 0 hour observed in the in situ incubation suggested that parts of the cell soluble might be used (oxidized) in the heating reaction. Heat treatment of PNM was effective in reducing N degradation by ruminal microorganisms.