The objective was to evaluate the effects of algae supplementation on milk performance and rumen fermentation in lactating dairy goats. Eight multiparous Xinong Saanen dairy goats in late lactation (3.9 ± 0.4 Parities; 208.5 ± 2.7 DIM; 61.5 ± 6.2 kg BW) were individually penned and randomly assigned to a replicated 4 × 4 Latin square design with 4 periods of 18 d. Four levels of algae power (Alltech International, Inc.) were supplemented in the basic ration: 0, 10, 20 and 40 g/d per goat. Algae powder was mixed with a small portion of concentrate and provided for goats before each feeding. Then left concentrate was given to goats followed by corn silage and alfalfa hay which was ad libitum. Goats were fed and manually milked twice daily in the pens before each feeding. DM intake (DMI) and milk performance were measured for 4 d following a washout period of 14 d in 18 d-period. Rumen fluid was collected for measuring pH value, NH₃-N concentration and VFAs profile at the last day of each period. Data were run by MIXED linear procedure and treatment means were compared by LSD test (P < 0.05). No significant dietary × time interaction effects was shown on DMI and milk performance. Goats fed 40 g/d algae produced 29.5% more milk than goats fed with 0 g/d algae, although milk yield was not affected by algae supplementation. Neither DMI nor milk components were changed by diets. In addition, no apparent milk fat depression was observed in goats with algae supplementation. Although pH value, NH₃-N concentration and total VFAs (TVFAs) in rumen were not influenced, changes of VFAs profile were provoked by algae supplementation. Lower molar proportion of acetate and higher of propionate were induced by algae (P < 0.05), decreasing the ratio of acetate to propionate (P < 0.05). In conclusion, goats with 40 g/d algae showed the potential to produce more milk than those with 0/d g algae, while not provoking milk fat depression. Considering VFAs profile was changed by algae supplementation, further analysis for the rumen microbial process and milk fatty acids profile should be measured.