The crystal structure of new YNi 4 Si-type RNi 4 Si (R=Y, La, Ce, Sm, Gd–Ho) compounds has been established using powder X-ray diffraction. The YNi 4 Si structure is a new structure type, which is orthorhombic derivative of CaCu 5 -type structure (space group Cmmm N 65, oC12).GdNi 4 Si and DyNi 4 Si compounds order ferromagnetically at 25 and 19K, respectively whereas YNi 4 Si shows antiferromagnetic nature. At 15K, DyNi 4 Si shows second antiferromagnetic-like transition. The magnetic moment of GdNi 4 Si at 5K in 50kOe field is ~7.2μ B /f.u. suggesting a completely ordered ferromagnetic state. The magnetocaloric effect of GdNi 4 Si is calculated in terms of isothermal magnetic entropy change and it reaches the maximum value of −12.8J/kgK for a field change of 50kOe near T C ~25K.