There was almost all cows suffered heat stress in hot and humid climate in most regions of China during summer. The objective of this study was to investigate the effect of biochemical fulvic acid (BFA) on heat stress and lactation performance in lactating cows. BFA is an aromatic nitrogen compound (Shenzhoulvyuanmuye Co., Hebei Province, China). Its molecular construction determined it can be chelated trace elements. Thirty multiparous Holstein dairy cows were blocked into 2 groups by parity, days in milk, milk yield (MY) and somatic cell counts (SCC). This research was conducted from July through August 2014 (49 d). Two groups were fed same TMR. One was control group (CG) without BFA; the treatment group (TG) was added 25g BFA per cow per day. The quantity of different cows’ parities is same in 2 groups (3 preparious cows, 7 s lactation cows and 5 third lactation cows). The averaged days in milk of TG versus CG were 150 ± 35 d vs. 149 ± 38 d (Mean ± SD). The MY of TG and CG was 38.4 ± 4.8, 37.9 ± 6.6 kg, respectively. The SCC of TG was 4.17 × 10⁴ compared with CG (5.06 × 10⁴). Cows were milked 3 times per day at 0430, 1230, and 2030 h. The MY, composition of milk, body temperature, blood samples, and respiratory rate were recorded. Data were statistically analyzed using the two-sample paired t-test for means procedure of SAS (version 9.2, SAS Institute Inc., Cary, NC). Although lactose, milk urea nitrogen (MUN), SCC, body temperature, and respiratory rate did not differ between TG and CG, milk yield (37.30 vs. 35.73 kg; P < 0.01) and concentration of milk fat (3.54 vs. 3.13%; P < 0.05) were significantly higher for TG compared with CG. However, the milk CP (3.29 vs. 3.18%; P < 0.01) of CG was higher than TG. In the meanwhile, concentration of serum GSX-px (356 vs 207 μmol/L, P < 0.05) was higher for TG compared with CG. These results suggested that adding BFA to lactating dairy cows during summer might increase milk yield, milk fat, relieve heat stress and not change the yield of milk CP.