In this study, we investigated suckling behavior and the distance between a foal and its mare as indicators of foal growth in Hokkaido native horses (HKD) during the first 40 days of life. Direct observations were made of 22 mare and foal pairs from two consecutive days 1 and 2, 5 and 6, 10 and 11, 20 and 21, 30 and 31, and 40 and 41 after birth by focal animal sampling for 3 h per day. Suckling behavior was continuously recorded, along with the terminator. The distance between the foal and its mare was determined using the instantaneous sampling method (1 min), and the percentage was calculated within 4 m while the foal was recumbent (DPW4FR). In the first week after birth, the duration and frequency of suckling terminated by the foal were negatively correlated with foal daily gains (duration, -0.49, p = 0.028; frequency, -0.53, p = 0.017). The DPW4FR and daily gain during 10-40 days after birth showed significant negative correlation (-0.47, p = 0.031). It is suggested that in HKD reproduction systems, suckling behavior termination by the foal and the distance between the foal and mare may be indicators of early foal growth.