The standardized ileal digestibility (SID) of amino acids (AAs) plus crude protein (CP), in addition to digestible energy (DE) and metabolizable energy (ME) concentrations, was assessed through two experiments on Saccharomyces cerevisiae yeast (SCY) combined with soybean meal (SBM) for gestating sows. SCY and SBM were subjected to experiment 1 for the determination of CP and AAs in terms of SID. Under a randomized complete block design, three dietary treatments were provided for a total of 24 Landrace × Yorkshire gestating sows (parity 2), with the distal ileum clipped by a T-cannula at gestational day 33 based on body weight (BW) (194.1 ± 7.1, 195.3 ± 8.5, and 195.3 ± 8.6 kg). SCY and SBM were used as the only source of nitrogen to prepare two semi-purified diets and a nitrogen-free diet was also utilized to examine CP plus AAs for basal ileal endogenous losses. The gestating sows were initially fed these diets for 5 d to allow for adaptation, and ileal digesta was collected 2 d later for analysis. CP and all AAs in SCY, except for Trp and Gly, showed significantly lower SID than those in SBM (P < 0.05). Among the essential AAs, the range of SID was 68.8% for Thr to 92.2% for Arg in dried yeast, and from 79.9% for Thr to 98.6% for Met in SBM. DE plus ME were measured via experiment 2 with a randomized complete block design on SCY and SBM. Eighteen day-35 Landrace × Yorkshire pregnant sows (parity 3) were allocated to three diets based on BW (233.3 ± 16.0, 233.4 ± 9.6, and 233.4 ± 10.3 kg). Three diets were adopted for the experiment, namely, a corn-based diet as well as two diets containing 20.2% SCY and 20.0% SBM samples. The full fecal collection method, comprising a 5-day adaptation period before a 5- to 6-d experimental period for quantitative urine and feces collection, was employed for metabolic trials. The DE and ME for SCY were remarkably decreased compared with those for SBM (3812 kcal/kg DM vs. 4264 kcal/kg DM and 3714 kcal/kg DM vs. 4157 kcal/kg DM), respectively (P < 0.05). No differences were observed in the apparent total tract digestibility (ATTD) of organic matter, CP, and gross energy between SCY and SBM, but ATTD was significantly reduced in SCY for acid detergent fiber, dry matter, and neutral detergent fiber by contrast with SBM (P < 0.05).