We have studied the magnetic, magnetocaloric, and magnetoelastic properties of LaFe 11.57 Si 1.43 B x compounds in the concentration interval 0 Ͻ x Յ 1.64 using magnetization and strain gauge techniques. The crystal cell parameters and Curie temperatures were found to increase linearly with increasing B concentrations up to ϳ0.1% and 9%, respectively. A positive magnetovolume anomaly of about 0.22% was observed in the vicinity of T C . The magnetovolume coupling constant was estimated to be approximately 3 ϫ 10 −3 ͓ B / Fe atom͔ −2 . Magnetic entropy changes at T C slightly depended on B concentration. A hysteresis loss of about ten times smaller relative to the base compound ͑x =0͒ was observed for x = 1.64. Therefore it was shown that the characteristics of the magnetocaloric effect of LaFe 11.57 Si 1.43 can be adjusted by a change in B concentration in the LaFe 11.57 Si 1.43 B x system. The relative importance of the variation in the volume of crystal cell and electron concentration on T C was discussed.