Bell pepper (Capsicum annuum L.) and Sweet cucumber (Cucumis sativus L.) are grown extensively throughout the world especially in temperate countries. Poor fruit-set as well as loss of reproductive structures due to moisture stress is one of the major barriers to tropical adaptation of bell pepper and sweet cucumber. Nitrobenzene is a combination of nitrogen and plant growth regulators, extracted from sea weeds that act as plant energizer, flowering stimulant and yield booster in crop production. The objective of the present study was to examine the effect of nitrobenzene on bell pepper and sweet cucumber yield to evaluate the optimum dose of nitrobenzene for economically better yield. The study was conducted at a farmer polytunnels located in Pilimathalawa and Athgala areas (WU1) in Sri Lanka. The experiment was laid out in a Completely Randomize Design (CRD) with four treatments randomized in three replicates. The treatments used for Bell pepper, T1 – Control (without Nitrobenzene), T2 – Nitrobenzene 15%, T3 – Nitrobenzene 20%, T4 – Nitrobenzene 25%. Treatments used for Sweet cucumber, T1 – Control (without Nitrobenzene), T2 – Nitrobenzene 10%, T3 – Nitrobenzene 15%, T4 – Nitrobenzene 20%. Accordingly, plants were established in drip-fertigated bags in the Poly tunnel and standard crop management practices were done throughout the study. Nitrobenzene was sprayed to the seedlings 20 and 35 days after sowing. Albert solution, 6: 30: 30 fertilizer mixture 20: 20 fertilizer mixture and Ca(NO3)2 were used as recommended fertilizers. Measurements were taken on growth parameters, reproductive parameters, Fruit setting and postharvest stages. The data obtained were subjected to the Analysis of Variance (ANOVA) procedure of Statistical Analysis System (SAS) 9.1. Duncan’s New Multiple Range Test (DNMRT) was performed to compare the differences among treatment means at p=0.05. According to the study findings, the Bell pepper performed better in 25% Nitrobenzene applied treatment while the Sweet cucumber performed better with the 20% Nitrobenzene showing significant (p=0.05) positive impact on postharvest quality of the fruits with extending the shelf life. Hence the overall study findings clearly revealed that the applications of higher Nitrobenzene levels are economically feasible to enhance the overall yield performance of Bell pepper as well as Sweet cucumber under greenhouse condition.