Recently, with increasing concern for sustainable agriculture and safe agricultural products, organic farming has become widely adapted as an alternative to conventional farming. This study was conducted to investigate the effects of earthworm casts (EWC) with 100~% organic compost on the growth and yield characteristics of fall-cropping potato (Solanum tuberosum L. cv. Dejima) in Jeju. The treatments consisted of seven plots: 2-, 4-, 6-, 8-, and 10-ton ha-1 EWC-treated plots, 1.2-ton ha-1 complex fertilizer (N-P2O5-K2O,~;10-10-14)-for-potato (CEP)-treated plot as conventional practices, and a control plot. The plant heights were greater in the plots where EWC and CFP were applied than in the control plot. Tuber diameter, number of stems per plant, and chlorophyll level tended to increase in the plots where 8-10 tons ha-1 of EWC were applied. The application of CFP and EWC showed an increment in the average tuber weight per plant, but there was minimal significant difference. The application of 8-10 tons ha-1 of EWC resulted in an increase in the total tuber yield (21.61-21.87 tons ha-1 ) as compared to the other plots. The highest yield of market able tubers was 69.8~% of the total yield from the 10-ton ha-1 EWC-treated plot. Consequently, with regard to the growth and yield characteristics of fall-cropping potato, the effects of EWC application were more favorable than the effects of the application of a chemical fertilizer.