<p>This work was done in order to evaluate the productive performance of fattening pelibuey lambs, carcass yield and the production costs when maize grain was replaced by grounded <em>Guazuma ulmifolia</em> fruit at 15 and 26% in their diet. An analysis of variance with a covariate design (initial weight and at slaughter) was used and the difference between means was compared with the Tukey's test (P&gt; 0.05). A chemical analysis of the fruit was performed along with <em>in vitro</em> and <em>in situ</em> digestibility. 27 male and female lambs were used at an average weight of 16.159 ± 3.615 kg. Food Intake, weight gain, feed conversion ratio and costs of the feed portions were evaluated. The animals were slaughtered at an average weight of 38.258 ± 3.684 kg. 4 male lambs were randomly assigned to each one of the treatments. Carcass and loin length, average leg, forequarters, spine, ribs and loin weight, warm carcass weight and yield; and price per kilogram of the warm carcass produced were obtained. The <em>G</em>. <em>umlifolia</em> fruit chemical analysis showed content of (%): 12.8 CP, 63.5 NDF, 54 ADF, 70 TND, 51 <em>in vitro</em> and 48.3 <em>in situ</em> digestibility, a=6.5 and b=37.5 and c= 0.025. Final weight in kg were for T1, T2 and T3 30.422 ± 4.790, 29.336 ± 5.802 and 28.456 ± 4.907 respectively; total weight gain were 13.911 ± 2.742^a and 13.489 ± 4.144^a 12.356 ± 2.339^b Kg (P&lt;0.05) in treatments 1, 2 and 3. Average feed conversion was 6.72:1 for the three treatments. The guasima fruit had a positive impact in the production cost there was a reduction per kilogram of produced meat up to 9 and 22% in T2 and T3 respectively. No significant differences were found between treatments for yield, carcass and meat production (P&lt;0.05). In T1 was 46.69 ± 2.91%, 49.06 ± 2.20% T2 and 45.73 ± 2.64 % in T3. It is concluded that under the conditions of this experiment, it is feasible to feed pelibuey lambs with <em>G. ulmifolia</em> fruit up to 15% in substitution for maize grain without affecting yield and improving the economic efficiency. </p>