Shanghai Observatory was charged by IAU Commission 19 to be data analysis center of optical technique (ACOT) until 1990. In 1988, a total of 14 509 sets of observations were obtained with 64 instruments in 15 countries (TABLEs 1–3). To ensure continuity, we use the same method for determining ERP as used before by the BIH. Raw and smoothed values of ERP in 5-day intervals are shown In TABLE 4. Yearly average of the errors in x, y and UT1-UTC are ±0.0129″ +0.0106″ and ±0.000995, respectively. The ERP values in 0.05 year intervals are shown in TABLE 6. The traces of the north pole and UT1-UTC are shown in Fig. 1. Comparison between TERS and ACOT is shown in TABLE 5 and Fig. 2. As measures of instrumental accuracies, typical fluctuation in a single measurement of latitude and UT, ϵφ and ϵT, were calculated. Stations with ϵφ better than ±0.10″ and/or ϵT better than ±0.0105 are listed in TABLE 7. We thank the colleagues of all participating stations for providing the data and particularly Dr M. Feissel for helpful suggestions.