The apparent diffusion coefficient (ADC) was associated with the onset of intrauterine growth restriction in singleton pregnancies. However, the correlation of ADC with selective intrauterine growth restriction (sIUGR) of monochorionic (MC) twin pregnancies remained unknown. In this study, we aimed to evaluate the association of ADC with sIUGR in MC twin pregnancies by exploring diffusion weighted MR imaging (DWI). Fifty-one MC twin pregnancies, consisting 19 cases of sIUGR and 32 cases without sIUGR, were re-analyzed by DWI. ADCs were quantitated from two regions of interest, surrounding the insertion of the umbilical cord of placenta for each twin. A rADC (ADClarger twin/ADCsmaller twin) in each placenta was also evaluated. Then ADCs and rADCs were compared between cases with and without sIUGR. The ADC in cases with sIUGR was significantly decreased compared with cases without sIUGR (1.846 × 103 vs 2.471 × 103 mm2/s, p < 0.001). The rADC in cases with sIUGR was significantly increased (1.346 vs 1.053, p < 0.001). The ADC decreases and the rADC increases in the placentas of MC twins with sIUGR, suggesting that diffusion in the placenta is restricted in pregnancies with sIUGR.