Abstract: The total carbon(TC), total nitrogen(TN) and nitrogen stable isotope ratio(15N) in macroalgal tissue were analyzed in conjunction with environmental variables in seawater to study the nitrogen sources and select effective macroalgal species along the Yantai coast. The results showed that macroalgal 15N values at the three sites were all between 6.18 and 10.99, indicating sewage effluent and/or aquaculture discharge being the dominant nitrogen sources. Sewage effluent was dominant factors affecting the nitrogen concentrations in the Moon Bay(S1). The nitrogen concentration at the Yangma Island(S3) was mainly related to aquaculture discharge and the Fisherman Wharf(S2) was affected by both sewage and aquaculture discharge. Ulva pertusa and Enteromorpha intestinalis in Chlorophyta are identified as effective indicators due to their high nitrogen uptake and minimal nitrogen fractionation.