The study presents the results of investigations carried out on a four-cylinder, four-stroke, direct injection diesel engine operated with tea seed (Camellia sinensis) oil biodiesel. The oil from tea seeds was extracted from grounded seeds using the Soxhlet extraction apparatus. The biodiesel was produced by transesterification of tea seed oil with methanol in the presence of a catalyst (NaOH). After being blended with regular diesel fuel (D), the fuel properties of tea seed biodiesel (B) was determined according to ASTM and EN standards. The fuel mixtures (biodiesel content at the volumetric ratios of 10%B-90%D (B10), 20%B-80%D (B20), and 100%B (B100)) were tested in a direct injection diesel engine at full load condition. The results indicated a decrease in the observed power output with the increase in biodiesel content in the mixture. Specific fuel consumption (SFC) values were increased depending on the amount of biodiesel in the test fuels. While CO and CO2 emissions were reduced, NOx emissions were increased with increasing biodiesel contents in the mixture. It can be concluded that, tea seed oil, as an agricultural crop, might be a reasonable raw material for the biodiesel production. It was also shown that, up to 20% volumetric content of tea seed biodiesel could be effectively used in fuel mixture serving the purpose of reduction in diesel fuel usage.