Information about the relative bioavailability (RBV) of l-methionine (LM; 100% l-isomers, 99% purity) compared with dl-methionine (DLM; a 50:50 mixture of d- and l-isomers; 99% purity) for pigs is limited. A 21-d experiment was conducted to determine the RVB of LM compared with DLM to maximize the performance of 7 to 13 kg weaned pigs. A total of 168 weaned pigs (Topigs; initial BW of 7.01 ± 0.04 kg) were assigned to 7 dietary treatments with 6 pen replicates (2 barrows and 2 gilts/pen). A corn-wheat-soybean meal-whey powder and fish meal-based basal diet (BD) was formulated using analyzed ingredient AA contents and published SID coefficients to contain 0.27% standardized ileal digestible (SID) Met and 0.54% SID Met + Cys but adequate in all other AA (1.35% SID Lys) and contained 2,498 kcal/kg NE. Dietary treatments included (1) BD, (2) BD + 0.05% DLM, (3) BD + 0.10% DLM, (4) BD + 0.15% DLM, (5) BD + 0.05% LM, (6) BD + 0.10% LM, and (7) BD + 0.15% LM. Data were analyzed by ANOVA using the GLM procedure of SAS. Orthogonal-polynomial contrasts were used to determine linear and quadratic effects of increasing levels of DLM and LM on response criteria, and the effect of Met sources. The final BW at d 21 (11.73, 12.49, 12.74, 12.68, 12.42, 12.65, and 12.82 kg for diets 1 to 7) and overall ADG (224, 258, 271, 269, 255, 268, and 272 g/d for diets 1 to 7) increased linearly (P < 0.05) by graded additions with both Met sources. The ADFI increased linearly (P = 0.03) by graded additions with DLM but was not affected by LM additions. The overall FCR (1.42, 1.32, 1.29, 1.31, 1.35, 1.32, and 1.29 for diets 1 to 7) improved (P < 0.01) linearly and quadratically by DLM additions and linearly by additions with LM. Performance responses (ADG, ADFI and FCR) of pigs fed diets supplemented with the same inclusion levels of DLM and LM were not different (P ≥ 0.487). Based on ADG as a response of Met intake, the nonlinear asymptotic model estimated the RBV of 89% (95% confidence interval: 49–128%) for LM relative to DLM. In conclusion, the bioavailability of LM relative to DLM is not different to optimize the performance of 7 to 13 kg weaned pigs.