In this study, the spacer-thickness-dependent room-temperature magnetoresistance (RTMR) is investigated in ferromagnetic/antiferromagnetic (FM/AFM) superlattices composed of 10 repetitions of La0.7Sr0.3MnO3/Nd0.6Ca0.4MnO3 [LSMO/NCMO]10. A series of superlattice samples with the thickness of the LSMO layer being fixed at 5 nm while that of the NCMO layer varied from 0 to 5 nm were fabricated using pulsed laser deposition. RTMR is measured at the fields from zero to 10 kOe with two different configurations, in plane (IP) and out-of-plane (OOP). At 10 kOe, RTMR varies with increasing spacer thickness of NCMO at both IP and OOP configurations. A maximum IP MR ratio of 16% at 10 kOe is found in the sample of [LSMO(5 nm)/NCMO(0.45 nm)]10, which is three times that for the pure LSMO film. Therefore, it is concluded that the inserting of the NCMO layer between LSMO layers can effectively tune the RTMR ratio, which might be related to the magnetic coupling between FM and AFM domains.