Abstract The methods to determine the material constants in ferroelectric Sm C* are summarized. The material constants dealt with are (1) the transition temperature, (2) the tilt angle, (3) the helical pitch, (4) the refractive index, (5) the spontaneous polarization, (6) the critical field to unwind the helix, (7) the elastic constant and (8) the viscosity coefficient. Based on the results obtained for 2-methylbutyl p-(p-n-alkoxybenzylideneamino) cinnamates (nOBAMBC), the importance of using properly prepared monodomain cells of high quality is emphasized by comparing our results obtained using the cells without surface treatment with others using the cells treated unidrectionally.