The aim is to evaluate amount of amoxicillin in the array of its injectable formulations from multisource marketed and commonly used in veterinary practice in Nigeria. The amount of amoxicillin in each of the 10  brands sampled was analysed using a high-performance liquid chromatography. Thereafter, percentages of the labelled amount of amoxicillin were determined and compared with 90-120%  specified in USP and IP. Samples G, H, and J contained 93%, 98%, and 108%, respectively of the labeled amount of amoxicillin, while B, C, and  A contained only 39%, 56%, and 58%, respectively. Again, samples I, F, D, and E contained 124%, 135%, 147%, and 413%, respectively of the labelled amount. Thus, only brands G, H, and J passed assay quality test (AQT) since the amount of amoxicillin they contained was within the specified USP and IP range, and are considered pharmaceutically equivalent, consequently, interchangeable for intravenous administrations. Whereas, brands A, B, and C failed AQT because they contained less than the amount of amoxicillin required, so even when used prudently there could be therapeutic failure, bacterial resistance, and public health implications. Similarly, brands D, E, F, and I could cause toxicity and high tissue residues because they contained higher than the required and labelled amount of amoxicillin. About 30% and 40% of the analysed amoxicillin brands contained less and more than the required amount of amoxicillin, respectively. However, 30% contained the amount within the specified range. Consequently, there is high rate of substandard amoxicillin injectable brands for veterinary use in Nigeria hence the need for regular monitoring.