The cross-education effect (CE) is the transference of neuromuscular adaptations from a single exercised limb to the contralateral nonexercised limb, which seems to differ between exercise modalities. We compared the acute CE of unilateral eccentric (ECC) and concentric (CONC) resistance exercises on neuromuscular function and force production changes of the nonexercised elbow flexors (EF). Healthy men were randomly allocated into ECC (n = 15) or CONC (n = 15) groups. The effects of control (CTRLCONC or CTRLECC: 30 min of sitting) and exercise conditions (5 sets × 10 repetitions at 80% of either ECC or CONC 1-repeti-tion maximum) of the dominant EF were measured. Maximal voluntary isometric contraction (MVIC), rate of torque development (RTD), corticospinal excitability (CSE), voluntary activation (VA), and peripheral factors were measured before and immediately after CTRLCONC/CTRLECC or CONC/ECC. Surface electromyography amplitude integral (sEMGi) from the biceps brachii (BB) muscle was monitored during exercise. Physical-mental demands (NASA-TLX) were assessed after exercise. ECC performed 26.2% greater exercise volume than CONC (P = 0.01). ECC showed lesser BB sEMGi (P = 0.04) than CONC in the exercised EF; however, it induced threefold greater irradiated sEMGi to the nonexercised BB than CONC (P = 0.04) during exercise. NASA-TLX was unchanged (P = 0.81). The nonexercised EF maintained MVIC, VA, cortical silent period, and peripheral factors after ECC and CONC (P > 0.05), but lower RTD was observed after ECC (23.5%–29.4%; P < 0.05) and CONC (10.8%; P < 0.05). Lower CSE at 75% of MVIC occurred after ECC (–17%; P = 0.02) compared with CTRLECC, which was correlated to RTD decreases (r = 0.45–0.56, P = 0.02–0.04). ECC induces acute contralateral reductions in CSE that are associated with decreases in RTD.