This study assessed the effects of non-tariff barriers (NTBs) on market participation for maize smallholder farmers in the major maize producing districts of Mbozi and Momba in Mbeya region located in the Southern Highland of Tanzania. A two-stage stratified sampling was used in selecting 240 smallholder farmers from the selected villages in two districts and interviewed. In estimating the effects of NTBs on market participation and quantity of maize sold by farmers, the two-stage Henchman model was used. Results showed that, NTBs and distance to market had negative effects on the quantity of maize supplied and market participation. This implies that, for every 100% increase in application of NTBs by the government could decrease market participation and sell of maize by 77% from smallholder farmers. However, ownership of assets and amount of harvest were found to increase maize supply and market participation by 68 and 2%, respectively. The study concluded that, application of NTBs policies in Tanzania could not increase supply of maize especially on surplus regions and districts. In contrast could discourage farmers’ market participation. Therefore, it was recommend that, government should eliminate discriminative NTBs and improve market infrastructures such as roads and storage facilities in order to increase farmers’ market participation.