Cholinergic crisis is an adverse effect of an anticholinesterase agent, which is one of the cholinergic agents. Cholinergic crisis may induce serious conditions such as breathing difficulties. Cholinergic crisis is often diagnosed by an abnormally low level of serum cholinesterase (ChE). However, ChE value is not an appropriate indicator of cholinergic crisis since it has a high inter-individual variation, even though its intra-individual variation is low. Therefore, an indicator with less inter-individual variation capable of preventing the risk of cholinergic crisis was investigated. The results of correlation test between ChE and serum albumin (Alb) showed a strong positive correlation; r = 0.778 in BCG method(Bromo cresol green method) and r = 0.766 in the BCP-improved method for Alb. In addition, the variations of Alb values are much lower than the drastic depression of ChE values in cholinergic crisis. Thus, it is considered that the ratio of ChE and Alb (ChE/Alb) can be a useful indicator of cholinergic crisis. As a result of ROC (Receiver operating characteristic) analysis, the ratios of ChE and Alb values using the BCG method (ChE/Alb (BCG)) were 20.7, 87.0, 156.8 for the Cutoff value, Likelihood ratio and Odds ratio respectively. When using the BCP-improved method for Alb, the ratios of ChE and Alb (ChE/Alb(BCP improved)) were 25.0, 93.7, 180.1 for the Cutoff value, Likelihood ratio and Odds ratio respectively. The ChE/Alb ratio appears to be an excellent indicator of cholinergic crisis diagnosis since it shows a high likelihood ratio as well as a high odds ratio.