The electrochemical behavior of antibiotic drugs, clindamycin hydrochloride (I) and its phosphate salt (II), on carbon paste electrode (CPE) is thoroughly investigated. Chemical and electrical parameters affecting the adsorption stripping voltammetry (ASV) measurements are optimized. Two different modes of sweep, viz., differential pulse (DP) and square wave (SW), are compared over a potential range of +400 to +1100 mV in the presence of 0.04 M Britton -Robinson buffer (pH 10) with an accumulation time of 30 s, scan rate of 100 mV/s, and pulse amplitude of 30 mV. The responses are linear over a concentration range of 86 -430 and 90 -813 ng/ml for I and 86 -516 and 172 -1030 ng/ml for II in the DP and SW sweep modes, respectively. The limits of detection (with correlation coefficients given in brackets) are as follow (ng/ml): 32.60 (0.998) and 90.73 (0.994) for I and 43.51 (0.997) and 83.02 (0.996) for II in the DP and SW sweep modes, respectively. The DP method has been applied successfully to determining the active ingredients in pharmaceutical preparations and in spiked urine with mean percentage recoveries of 99.24 ± 2.14 and 98.66 ± 2.38, respectively.