This experiment was conducted to study the effect of feeding soybean meal (SBM), soybean oil plus SBM, raw soybean (RSB) and extruded soybean (ESB) on the nitrogen (N) metabolism in the rumen, organic matter (OM) and nitrogen flow to the abomasum in lambs. Results obtained from the present study are summarized as follows: 1. Ruminal pH, NH₃-N and total volatile fatty acid (VFA) were not affected by soybean sources. Isobutyrate (P$lt;0.01), isovalerate and valerate (P$lt;0.05) were highest for RSB and lower the heat processed diets. There was no dietary effect on ruminal OM digestion and flow to the abomasum, but a consistent trend for higher OM flow with ESB diet was observed compared with RSB diet. Nitrogen retention (% intake) was not affected by treatments and ranged from 39 to 42%, and urinary N excretion was lower for ESB diet. Soybean oil supplementation to the SBM diet tended to decrease N retention. Nitrogen flow and non ammonia nitrogen (NAN) flow to the abomasum were similar among soy-bean sources. Nitrogen composition of rumen bacteria was highest for SBM diet (P$lt;0.05) and levels of essential amino acid, notably lle, Met and Phe, were tended to be higher for SBM diet. Ether extract content in abomasal whole digesta was lowest (P$lt;0.05) with SBM diet, and Met and Asp were highest (P$lt;0.05) with ESB diet.