This experiment was carried out to study associative effects of the chopping of hay at two stages of maturity on the nitrogen balance, nutritive value and energy balance in goats fed rye hay. Twelve Japanese goats were fed rye hay ad libitum in a unchopped form or chopped to 2 cm of chopping lengths. They were grouped into tetrads as follows: B I and B II were fed with unchopped and chopped hay at the boot stage, H I and H II were led unchopped and chopped hay at the heading stage respectively. Nitrogen intake(NI) and digestible nitrogen (DN) were significantly higher(p$lt;0.05) in groups (B I and B II) fed hay at boot stage ttran in groups(H I and H II) fed hay at heading stage. However, the differences corresponding with the chopping of hay were not accepted at both growth stages. Nitrogen losses as feces(FN) and urine(UN) were similar to the results for NI and DN, RN was high in groups(B I and B II) fed hay at the boot stage, although there was no significant difference (p$gt;0.05), but that had little differences in relation to the chopping of hay at both growth stages. On the other hand, the ratio of FN to NI wars higher in H I and H II than in B I and B II, while there were no great differences(p$gt;0.05) between unchopped hay and chopped hay at both growth stages. The ratio of UN to NI was similar of both growth stages. GE in groups(H I and H II) fed hay at the heading stage were significantly higher(p$gt;0.05) than those in groups fed hay at the boot stage. However, DE and ME were greater in groups(B I and B II) fed hay at the boot stage, although there was no significant difference for ME. TDN and DCP were also significantly higher(p$gt;0.05) in B I and B II than in H I and H II. No differences were recognized corresponding to the chopping of hay at both stages for GE, DE, ME, TDN and DCP. EI was a little lower in H I and H II than in B I and B II but was not significant. Energy lasses in FE, UE, CH, and HP did not differ in relation to the chopping and growth stage of hay. RE was 148.9, 108.9, 23.2 and 51.9 MJ/㎏W^(0.75) for B I, B II, H I and H II respectively, and thus RE in groups(B I and B II) fed hay at boot stage were significantly larger(p$lt;0.05) than those in groups(H I and H II) fed hay at heading stage. But there were no effects of the chopping of hay at both growth stages. RE was closely related with dry matter and energy intake(p$lt;0.05), especially with digestible dry matter and digestible energy intake(p$lt;0.01).