For the last three decades or so, the use of mathematical techniques in management has been gaining grounds. One of such techniques in use in the field of commerce and management is "Financial Ratios". The objective of this study was to investigate the validity of financial ratio analysis as a performance evaluation technique. The study was concentrated on Jos International Breweries PLC over a three year period - 1988 - 1990. The company's financial statements for the period under study were subjected to ratio analysis to see if ratios can give the financial analyst advance warning as regards the future financial position of a company. The procedure followed for collecting data for this project was through the primary and secondary sources of information. The primary sources of information were the audited financial statements of the company for the years 1988 - 1990, and personal interview of some key staff of the finance division. The secondary sources of information was through previous write-ups on financial ratios - journals, magazines, newspapers and text books. Having analysed the data collected, it became clear that financial ratios can reveal to a manager areas of financial difficulties thereby enabling him to take control measures. The conclusion is that financial ratios are one of the most accurate and reliable evaluative tools available to the manager in assessing the future prospects and difficulties of his/her company.