Sage (Salvia officinalis L.) is among the herbs and spices grown for culinary uses is increasingly becoming important in Kenya. Its leaf productivity is however often limited by nitrogen and phosphorus, which are deficient in many Kenyan soils. The problem is even exacerbated by irregular rainfall in most parts of the country where it is grown, thus necessitating irrigation. The objective of this study was therefore to determine the effects of nitrogen, phosphorus and watering regimes on vegetative and leaf yield of sage. The experiment conducted at the Horticultural research and teaching Farm of Egerton University, was laid out in a three factor Strip Plot arrangement in a Randomised Complete Block Design (RCBD, with three replications. The treatments consisted of nitrogen (N) supplied as urea (46% N) at four rates; 0, 40, 80 and 120kg N/ha while phosphorus (P) was supplied as Triple Superphosphate (46% P2O5) at four rates; 0, 30, 60 and 90kg P/ha. Watering regimes included W1= Watering to field capacity once after every week, W2= Watering to field capacity once after every two weeks, and W3= watering to field capacity once after every four weeks. Nitrogen was assigned to the main plots; watering to the strip plots, and P to the sub-sub plots. The experiment was conducted in three trials; trial 1 (June 2011 – October 2011), trial 2 (October 2011 – February 2012) and trial 3 (March 2012 – May 2012). Data were collected on plant height, Leaf Area Index (LAI), leaf fresh and dry weights. All data were subjected to the analysis of variance (ANOVA) and where F test was significant; treatment means were separated using the Tukey’s Studentized Range Test at P ≤ 0.05. Results indicated that nitrogen applied at 80 kg N/ha, P at 60 kg P/ha and watering once after every two weeks gave the highest plant height (50.67 cm, 60.58 cm and 46.50 cm in trials 1, 2 and 3, respectively), and leaf fresh yield (27.10 ton/ha, 16.03 ton/ha 14.67 ton/ha in trials 1, 2 and 3, respectively). There is need however for economic evaluation of these practices before they can be recommended for use in Kenya.