The aim of this work was to determine the net energy requirement for maintenance (NE_m) of commercial crossbred beef heifers. Six crossbred (Bos taurus x Bos indicus) heifers cannulated in the dorsal sac of the rumen and with an initial body weight (BW) of 414 ± 52 kg were used. Heifers had an adaptation period to ration and management of 28 days. They were fed daily with a maintenance ration based on chopped Taiwan grass (Pennisetum purpureum) and a supplement, except on the days of fasting heat production (FHP) measurements. Cattle were fasted with the washed-rumen technique. All contents (dry, liquids) in the reticulo-rumen were evacuated through the rumen cannula. After rumen evacuation, heifers were fasted for 12 h and subsequently, oxygen (O₂) consumption was measured for 23 h in open-circuit respiration chambers. FHP was calculated by the energy equivalent of each liter of O₂ consumed (19.7 kJ/L). FHP measurements were made 4 times per animal (4 periods) with 13 days of rest between measurements to reestablish feed intake. Mean O₂ consumption and FHP (n = 24) were 1,587 ± 231 L/d (CV = 14.54%) and 399.6 ± 58 kJ/kg^0.75/d (CV = 14.69%), respectively. The data derived from the present study may contribute to the improvement in the estimates of net energy requirements for maintenance of commercial crossbred beef cattle in the tropics.