The objective of the study was to determine minimum horizontal distance (HD) between perches for laying hens using qualitative and quantitative behavioral analysis. A real-time monitoring system was developed to record hen’s perching behaviors, such as the number of perching hens, perching duration, perching trips, and the pattern of perch occupancy. Three groups of sixteen W-36 laying hens (68 weeks old at test onset) with prior perching experience were used. For each group, hens were kept in an enriched wire-mesh floor pen (1.2×1.2×1.2m) equipped with two parallel perches (15 cm perch space/hen). The HD between the perches were varied sequentially at 60, 40, 30, 25, 20, and 15 cm; then varied again in a reversed order. The minimum HD that led to no significant change in hen’s perching behavior was determined. Results showed that reduction of HD to 25 cm did not significantly restrain hen’s perching behavior; however, HD <25 cm significantly reduced the proportion of perching hens. When HD was insufficient, more perching trips occurred during the 45 min prior to dark period, indicating increase in perching competition. Meanwhile, hens perched interlacing with one another and tended to perch outwards from the opposite perch or hens during dark period, which might be a strategy to use the perch more efficiently. Horizontal distance of 60 cm increased the perching duration and reduced the perching trips during light period; however these two behavioral responses were not affected by HD <60 cm. Therefore, 25 cm is suggested as the minimum HD between laying-hen perches, 30 cm being preferable, and large HD’s such as 60 cm not advisable.